It's hard to make decent recommendations when you don't really detail the nuts and bolts of your usage needs. You don't talk about how many minutes of airtime you use per month, or the best network for coverage in your area, or whether you need post-paid billing, or how much data you need, do you need domestic calling only or both domestic and international, or whether you need off-network roaming either domestically or internationally, and what sort of handset you own and whether it's carrier unlocked and/or actually supported and compatible on other networks here in the post 4G VoLTE world, as switching might require a different handset. You also don't mention whether you actually need true mobility with your phone service or not.... like, are you stationary in an office 90% of the time, or are you constantly out in the field traveling?
The thing is, with business plans, especially business plans with heavy phone minute usage, you typically gotta actually pay for what you need. There really aren't any MVNOs (mobile VIRTUAL network operators) that're going to truly deliver on their promise of "unlimited" minutes, as most of them have details in their terms of service agreement that defines "unlimited" as some nebulous non-number that's around the "average".
If reliability is also important, it's worth noting that there's at least 3-4 tiers of network tower priority with service. MNO (mobile network operator) postpaid (which is what you have) is top tower priority, and prepaid pseudo-MVNO MNO brands like Visible (Verizon), Cricket (AT&T), and Metro (T-Mobile) are second tier, and some larger postpaid MVNOs sometimes get second tier priority, but not all. Most prepaid third party MVNOs (RedPocket and US Mobile for example) get third tier priority or lower. This means, the more congested the tower, and the cheaper and more removed from the MNO the MVNO is, the lower the priority of service you'll get on what is likely already oversaturated towers. Most of the time, this isn't a big deal since overall mobile network service is crappy at best, and you won't run into problems, but times of natural disaster or massive network load from massive concentrated population events can cause problems on local infrastructure leading to dodgier service. It's also worth noting that most MVNOs have data speeds capped out at slower than the network as well, usually under 10Mb/s, and there'll be massive throttling on data overages down to around 100kb/s as most all of them promise "unlimited" data with high speed data packages up to a certain size. You'll also lose stuff like account comping for network outages like what AT&T had a few days ago with MVNOs. Lastly, it's better to go with bigger, more well known MVNOs over smaller outfits, as sometimes MVNOs can just... shut down without warning. So, higher risk, but not common. Still should be worth being aware of if you're deeply risk adverse.
Many MVNOs can have better customer service than the MNOs, but most do not. One of the ongoing problems within the industry is the fact that people are just willing to tolerate lousy to zero customer service. When paying big money for a business account with Verizon gets you treated like a meth-addled hobo, there's not much to say. Dealing with AT&T or T-Mobile directly with a business account isn't gonna be much of an upgrade, if we're being honest, and AT&T's customer service has gotten so bad, that if I have to use their network or infrastructure, I'll go out of my way to pay for someone else to be a middle man between me and them, even if it potentially costs more. Line must go up for the investors living off of their stock portfolio so they don't have to work and the C-suite demands their golden paycheck lifestyle, so the employees and customers suffer with cheap and lousy tools, poor service, and a gross undervaluing of labor. Enter
enshittification, which isn't just for online platforms.
But, yeah. Hard to make a reasonable recommendation without knowing more. Unfortunately, there's really not any realistic suggestions for better/cheaper without knowing more. If you're mostly stationary, it's worth noting that "wired" services will be inherently more robust and reliable than wireless, and a lot of VoIP options now have call hunting where you can have the number forward and ring your cellphone as well. It's nearly a slam dunk to use VoIP if you're mostly in one place, especially if you have solid and reliable internet, doubly so if it's FTTP (fiber to the premises).
As for advice without knowing more? Read the terms of service agreements and fine print with whomever you're looking to switch to. Again, READ THE TERMS OF SERVICE AGREEMENTS AND FINE PRINT WITH WHOMEVER YOU'RE LOOKING TO SWITCH TO! When it comes to fine print and weasel words like "unlimited", less is more. Learn what your actual average and worst case usage is month to month, and talk with sales and support with whomever you switch to and ask pointed questions about what the best plans would be for that, and compare your notes and their suggestions with their legal boilerplate. It's worth noting that not all MVNOs have the same policies with payment issues like what you have, so it's important to check that, because some providers you'll lose your number within days of payment failure, where others will give you weeks. Accept the irrational reality that different data plans may provide different definitions of "unlimited" voice calling, and you might potentially have to pay for more data than you'd otherwise use to offset that issue. Nobody really offers "business tier" services anymore either, outside of the major carriers and ISPs.
Ultimately, don't be afraid to pay for what you need. Again, don't be cheap, pay for what you NEED. Prioritize your needs, and be willing to pay for what's the most important.
(Most MVNOs mentioned from this point technically qualify as postpaid MVNOs or MVNOs that offer postpaid plans, which are less likely to have boilerplate terminating your account for heavy voice services in the terms, outside of heavy roaming on partner networks, if they offer roaming at all. You're likely to have higher network priority than most other MVNOs, and they'll have plans that'll probably dovetail into more of what you're wanting.)
Anyway, outside of that and not knowing more, look into postpaid MVNOs like Consumer Cellular. They're AT&T/T-Mobile based, but don't provide international roaming. Their customer service is domestic, and good enough to keep the AARP blue-hairs happy. They don't really do business accounts, though.
If you want international roaming, the only alternative to the major carriers will be Ting (T-Mobile/Verizon) and Google Fi (T-Mobile). Dish owns Ting now, and customer service is but a shadow of the Tucows days. As for Google? Customer service? What customer service? Google doesn't pay humans for such things. That said, there's less to screw up with their billing and plans. Neither of these technically provide business tier services, either.
Beyond that, the only large MVNO I know of that specifically specializes in business plans only is Clearway (AT&T, Verizon), a subdivision of Tracfone, which is a subdivision of Verizon Wireless. Tracfone customer service? Yeah, so the usual problems with billing and support that somehow makes Verizon look saintly in comparison. It's prepaid. There's no frills, no roaming, bottom tier tower priority, but the only way you can exceed their per month voice minute cap is to make calls 24/7 with other calls on hold with call waiting during that 30 day limit. Their terms clearly cap 30-day period usage at 60GB of data, calling for over 43,200 minutes, or sending over 30,000 text messages (or 3,000 over a 24-hour period)... which realistically is one of the least bastardly terms you'll find with any of the Verizon/Tracfone sub-brands.
Hope this helps.
