Pre-authorization and now no pay

in February 2015 I had to undergo a minor procedure. The doctor called medical aid for pre authorization which was given. They claim that after receiving the test results, they changed the codes without telling anyone. The procedure was done and Resolution refused to pay the doctor because he used the codes for the pre authorization. The doctor said he would not change the codes because this is not what he had done. Now I have been handed over for the bill. The call centre is pathetic, I had to call back several times and today I called 3 times holding on at some point for 16 minutes. Marlene promised to send me information and escalate to a supervisor, but never did