take tennis lessons, and you look online and the court accepts paypal, but not venmo. But, you are OK with that, because you use paypal. So, you schedule and show up and the private coach shows up to teach you, and does so. But, he doesn't accept paypal, only venmo. So, you decide "I'm so mad, you don't accept paypal, so I'm not going to pay you". You fight over it for a year, and then he gets fed up with fighting with you over it, so he just writes it off.

You received a service, a 3rd party that pays for your care, if you go to the right location, said they don't contract with the ER physician. They still gave you a service. You chose not to pay it. That's on you.

You probably never thought about it this way, and so I'm not trying to be super harsh. Take a look from a different perspective. Sure, sucks that your insurance company didn't contract with the physician, but, that is life in every facet of the US economy.