Ambulance provider is billing me after already being paid by insurance

I took an ambulance ride to the hospital a few months ago and got the bill a few months after. My insurance is supposed to be 100% coverage for this based on what I was told by one of the service reps when I called my insurance. My insurance paid the ambulance provider "in-network" rates even though they are out of network.

But the ambulance provider is now coming back at me and saying I owe $500 on top of that because they are a "federally mandated" provider (from what I could google, >70% are anyway) and they are saying their rates a set by the state of CT.

I dont know if I really have to pay this or if my insurance or the ambulance provider are just trying to pass the buck here and get me to pay something I may technically not have to.

Ive googled and I found that this kind of thing used to be part of some "no surprise billing" bill in congress that later got removed before it passed, so it kinda has me even more curious as to whether this is my responsibility to pay or not. My insurance created an entirely new claim where it showed I owed nothing in addition to the original where I owe $500 which seemed kinda sketch and they said the ambulance provider is responsible and the ambulance provider is pointing the finger back at my insurance.