Hospital Billing during period of insurance overlap.

I have an issue with insurance in washington state. Last year I was between software contract jobs and was covered by WA state apple health, medicaid. I then started a new job and there was a period of time for about 1 month that I was covered by both my new employers insurance, (Premera), and Medicaid (Molina). During the period of overlap, I had an endoscopy done to rule out esophageal cancer since I was scared about my health, and it would take months to get a new primary care, referral to a new GI specialist, and get scheduled for an endoscopy again. The endoscopy was done at a facility that I had been using during my unemployment, and was in network with medicaid (molina).

Well, almost a year later I get a bill of more than $5000 because apparently both insurances denied payment.

Digging into this, it turns out that even though Molina was in network with the provider, Premera was not. Molina originally paid the full amount, but then they reverted it under (Coordination of benefits). They took months to hash out who was the primary. Then, when Premera was finally named primary, they denied as out of network. The remaining bill went to Molina, who denied it because it took so long for the two insurances to coordinate benefits, that it was passed the timely filling deadline. How is the provider’s failure to coordinate benefits my fault? I have called the provider, and the two insurances multiple times to get a resolution, but everyone keeps passing the buck, and blaming the other parties. Noone will resolve this, and I keep getting the run around. I have appealed with the provider already, and they keep telling me to wait 6 weeks for resolution, only to get the same bill again.

What protections do I have? Does this fall under the no surprises act or medicaid protections? Given they didnt bill me for more than a year, by the time I became aware there was a billing issue to begin with, it was way passed the timely filling deadline. What should I do? Who should I contact to try to get this resolved?

Right now, I am again between jobs after a layoff (software industry) so my gross income currently is only from unemployment, about 4k a month. I am married, filling jointly with my spouse who is also between jobs.