BCBS . . . ugh. They were actually issued a gigantic fine by my state a couple of decades ago (and maybe more recently as I don't follow that news closely) for not paying for things they were supposed to cover. Read more if you care to find out how I have learned to combat it.
I had twins at a hospital that was "in network", but some of the doctors who worked at the hospital were apparently "out of network." BCBS was supposed to pay anyway, and they certainly were supposed to pay for care for both infants and not reject everything as "duplicate billings," but the runaround is their game. That scene from the movie The Incredibles pretty much nails it. Anyway here is the game plan:
Document, document, document. Every time you call either the doctors office or BCBS, write down the date, time, and name of whom you speak with. Repeat their name to them and make sure you spell it correctly. Write down what they say their action will be or what needs to be done (most often this will be to refile the claim a certain way, but sometimes they say they will call the other party to resolve it.) I used to go round and round with them 3-4 times. That gets old. In the most ridiculous case, I went round and round more than 6 times over many months with BCBS who keep alternating their reasons (literally switching back and forth between two technicalities about how it was filed) for not paying the anesthesiologist for my C-section. In that case I ended up sending my stack of documenting paperwork to the state department of insurance. My state has an online complaint form and then you just mail in supporting documentation; you might even be able to scan and attach it online now. They called me to say they were investigating, and BCBS paid the claim within 2 weeks of the investigation opening.
I am at the point where I just call the insurance once and the doctor once. I keep my notes carefully. If that doesn't resolve it, and I am certain it should be covered, then the next time I get a bill or statement of benefits denying a claim, then I send the insurance company a copy of the most recent nonpayment statement with a written letter explaining that "I have made a good faith effort to resolve this" and that "If this does not get paid within the next 30 days, then I will file a complaint with the state Department of Insurance." That leads to payment 100% of the time so far.
Good luck!