Doctor switched out of insurance right AFTER procedure. Even had someone on the phone confirm that it was in-network and I would be fine. Except, my insurance keeps saying I may owe the provider. What do I do?

I had an endoscopy in March of this year, about two weeks later my doctor switched to another group and went out of network for me. So when the claim was processed it automatically was denied because of this. However, I called my health insurance (UHC Oxford Metro) and they confirmed that the procedure was in network at the time it was done, and even said there was some type of agreement with the doctor about the costs (there was a term for this, but I forget). He said I would be fine and to just wait for the claim to get reprocessed, which would take about two weeks.

In the meantime I also called my provider and they said they didn’t have a bill for me, and that everything was set. Fast forward two months and I finally receive a statement in the mail from my insurance saying that they denied my claim again and that they weren’t covering my benefit.

However, I still haven’t received a bill from the provider, and at this point I feel like it’s risky to poke the bear and call my provider again because they may look into it and realize I do need to pay. Considering I don’t have any bill and just a notice from my provider that I may owe $1,800, should I even do anything at this point?