My physician's office is fucking me over..

I recognize part of this likely goes outside the scope of this group, but I’m looking for some guidance here on how to proceed.

I had health insurance through my employer as of 9/2021, but then resigned from said employer 9/10/21. I was aware that my health insurance lasted up to a month post-separation, so upon my visit to my physician’s office on 11/2/21, I made sure to express that I didn’t have insurance and that the visit would be an out-of-pocket visit — which was $60 compared to my normal copay of $30. I still have the receipts and statements to verify this.

My issue is that my physician’s office’s receptionists are.. let’s say, making some awful errors. This session was billed to my former health insurance Blue Cross/Blue Shield of NC, who then paid the bill; then, about 5 months later in April, sent me a bill stating I didn’t have coverage for the visit, and since they paid the billing sent to them, that I owed BC/BS what they paid to the physician’s office. Obviously, this is where I contact the physician’s office to simply rectify the situation since this is a pretty simple and straightforward case.. but, as you can guess, I wouldn’t be posting here seeking advice if it were that simple.

I immediately call the physician’s office and they don’t pick up. I don’t mean once, I don’t mean twice, I don’t mean 15 times, I mean they actually just don’t pick up the phone. Ever. There are multiple departments with options to leave messages — literally not once does anybody ever respond to the 10+ voicemails left. I physically go up to the office on 3 different occasions and tell them of my situation and am told that the billing department consists of one person, who works remotely and part-time, and was assured somebody would contact me in “up to 3 business days”. Nope, didn’t happen either.