Hospital keeps sending Mr designation of authorized representative forms, should I sign?

Quick background. My wife and I got into a car accident last year. No injuries but ambulance took my wife to nearest hospital (in Los Angeles). They did a bunch of routine tests and scans to confirm nothing serious has occurred. I have very good insurance from United healthcare. Hospital was out of network (because of course it was!). I expected everything to be covered as emergency with $250 deductible to pay as has happened in past ER situations. Bill for $65k arrived from hospital. Clearly they were trying to balance bill which is clearly against the “no surprise bill act”. I called insurance and they confirmed. I read the act to the hostel billing dept and they claimed they knew nothing about it. Again insurance rep said this often happens and hospitals just try to see if they can get people to pay and just ignore them. They stopped sending bills but start sending désignation of authorized representative forms by certified mail for me to sign. I asked insurance rep what to do and they said I could sign or not, up to me. Hospital was trying to appeal but because of “no surprise bill act” insurance company and I had no requirement to pay the balance. I asked what happens if I don’t sign and insurance seemed to indicate it was no big deal. I don’t like hospitals trying to rip me off when clearly they are in the wrong (this is not my first rodeo dealing with these situations) so in minded not to waste my time and postage filling out the form in this case. Any reason I should fill it out other than being nice to the hospital. Insurance rep said the hospital could appeal as many times as they like but they weren’t going to pay. Maybe if the hospital were to call me and talk to me like a human I might be more inclined to help them, but they haven’t.