MTN OVERCHARGES

I HAVE BEEN TRYING SINCE MID OCTOBER TO RESOLVE OVERCHARGES RELATING TO MY TWO CONTRACTS. I HAVE SENT 14 SEPERATE EMAILS DETAILING THE OVERCHARGES, ALL OF WHICH WERE ACKNOWLEDGED BUT NO PROGRESS. EVENTUALLY I RECEIVED A PHONE CALL ADVISING THAT THE MATTER HAD BEEN RESOLVED BY THE BILLING DEPT AND THAT I WOULD RECEIVE A CREDIT ON MY NOVEMBER BILLING. HAVE NOW BEEN CHARGED FOR NOVEMBER WITH NO CREDIT PLUS AN EVEN HIGHER INCORRECT CHARGE. IMPOSSIBLE TO GET THE NAME OR CONTACT DETAILS OF A SUPERVISOR OR SENIOR PERSON