Unfortunately, I'm in the middle of the same experience.
My frustration is not with MMM for the recommendation of Credibe, or even Credible, but with the lending institution.
For those unfamiliar, Credible works by gathering your general information, then scraping available lenders to get estimated rates. Credible presents the option to you, and you choose the terms and lender. Once you choose credible creates an account for you, and transfers your profile data to partially complete the application. Now you are dealing with a lending institution. If they are terrible, then it isn't MMM's fault, or even Credible's fault.
For example: I want to refi some student loans. I read about Credible on MMM and am trying it. I entered data to Credible about 7 weeks ago. Credible presented several refi options. One was with PenFed for 3.45% for 8 years. I wanted that, so Credible created an account for me and gave me the login and password. I opened my account with PenFed. Of course PenFed is a bank/credit union. They don't originate loans. PenFed then shipped me to Purefy, the actual lender.
MMM -> Credible -> PenFed -> Purefy
Purefy has been as OP described, or worse. My "rep" didn't answer phone calls, emails, or texts. The only way I got information was by calling the main line and waiting on hold until someone answered. Once I was talking with someone they told me they needed more documents, then more documents, which I sent. Finally, they said 50% of my income didn't qualify, so they would offer me 3.96% for 8 years.
I await the final paperwork. It is not 3.45%, but 3.96% is silly cheap money. I have looked around a little bit more, and can't see anyone else even teasing a 3.45% rate, so I'm moving forward with the 3.96%. Frankly, I wish I could borrow more at that rate. I'm willing to do the back-end work to enable me to refi to that rate.
After reading the OP post, I'm going to call my credit union and my mortgage broker to see if they can meet or beat the rate.