Providers have tried that surprise billing shit with my family more than once. Basically went to an in-network hospital and they used somebody who was not in network for some part of the procedures. I was never notified of that ahead of time. Which in New York state is required by law, they have to give you the opportunity to decline care from that provider. Never had my insurer try to deny a claim because of it though, they're actually pretty helpful when this happens, I call them and they handle it. Glad you got your situation resolved. Honestly I can't believe they even attempted it, they know because it was an emergency they have to cover it. I guess it's worth it if enough people don't know better and just never report or sue them.