Insurer pre-auth approved my surgery in writing then denied the claim after - now Im on the hook for $22k

Had an outpatient knee procedure done in February. Before scheduling, my surgeons office called my insurance, got a pre-authorization number, and the rep on the phone confirmed coverage. I have the auth number written on the paperwork. We even got it in a letter mailed to me.

Surgery happens, recovery goes fine. Then in April the bills start showing up. Insurance denied the claim entirely, saying the procedure was "not medically necessary" based on chart review. The hospital is now sending me $22,400 in bills and threatening collections by August.

I called the insurer four separate times. Three different reps gave me three different explanations. One said the pre-auth was for a "different procedure code." Another said pre-auth doesnt guarantee payment. The third said i should appeal but the appeal deadline was apparently 60 days from the denial notice which i swear i never got in the mail.

I dont even know where to start with this. The hospital wont negotiate while its still in appeal. My surgeon is sympathetic but says his hands are tied. Anyone been through this exact mess? Is there a state regulator that handles pre-auth bait and switch cases?