I agree with trying to find hospital ombudsman and/or local news station investigative reporter.
I was escalated to billing supervisor of hospital and got her email and I told her they needed to recode and resubmit the bill. I further told her we would only pay copay after they recoded and resubmitted. I followed up with an email reminding them to recode and resubmit so we could pay our copay AFTER they get insurer to pay on properly coded & submitted bill.