Yes, easier said than done. We’ve got strategies for you.
Never hesitate to report the offending party to the appropriate state level consumer protection agency, for example your state’s department of insurance. I have had much success in getting insurers to toe the line by doing that. It works better in leftist blue states with huge bureaucracies (looking at you California!).
I'm a medical coder and you would not believe the frequency of plain old human error coding mistakes that go on bills. Worse, the pressure physicians and hospitals put on coders/billers to "upcode" (code for something more extensive and expensive), slap on a ton of questionable diagnoses, or bill for something that didn't happen is intense. Never never never pay a bill without verifying every code (diagnoses and procedures).