Premera denied our claim then strung us along til we couldn’t appeal any more

My apologies if this doesn’t belong here, if it doesn’t could you point me in the right direction?

My son was born in January 2021 in an in-network hospital. The hospital put my son in NICU, without even asking us, and it turns out the NICU itself AND the doctor were both out of network so we received two bills for both the NICU room and the doctor who was caring for my kid. We received a balance bill on 4/2022. I’ve been going back and forth all this time with the provider and the insurance company about it, saying it should be processed as in-network. The provider filed an appeal on their behalf and it was denied. Now Premera is saying we are past the window for filing an appeal and it is our responsibility to pay. I started looking into filing a complaint with CA insurance commissioner and a dispute with the No Surprises Act, does anyone have any suggestions or recommendations? I really feel swindled right now, every time I called Premera they kept telling me “oh we will look into it and call you back” I feel in an effort to get past the appeals window because they never called back or followed up on our questions and claims. I thank you in advance for any help or suggestions you can offer.