Why yes they are.  If they sign on to be a list of those participating doctors then they are bound by the rules that the health insurance company sets.  They - the doctors - enter in to a contract with the insurance company and they agree to these terms.  You need to advise the insurance company of what is going on here and file a complaint. This is a form of insurance fraud and you need to also report it to the insurance department.  I would call the doctor's office and explain that you have become aware that there has been a discrepancy in the charge and that you wish it reimbursed as soon as possible.  If they do not comply send a letter and copy the insurance department.  Good luck.