UNAUTHORISED BILLING OF CONTRACT

I CURRENTLY HAVE A CONTRACT WITH CELL C FOR MY BLACKBERRY Z3.AS YOU MAY KNOW THIS IS PART OF THE NEW RANGE OF BLACKBERRY 10 SMARTPHONES WHICH UTILISES NORMAL DATA. DESPITE THIS,I WAS ALLOCATED FAIR USAGE DATA AND AS A RESULT MY DATA WAS BEING CHARGED ONTO MY CONTRACT.THIS IS THE THIRD TIME THAT THIS HAPPENED AND WAS COMPLETELY UNAUTHORISED. I WENT DIRECTLY TO A CELL C STORE CLOSEST TO ME(PAVILION) AND THEY WERE NOT ABLE TO ASSIST ME AND STATED THAT I SHOULD CONTACT CUSTOMER CARE SERVICES. I DID THIS THREE TIMES AS WELL BUT NO ONE WAS ABLE TO ASSIST ME ,DESPITE LODGING A CASE.I WAS TOLD THAT I WOULD BE CONTACTED WITHIN THE NEXT 2 WORKING DAYS AND I WAS NOT.I AM FULLY AWARE OF MY CONSUMER RIGHTS AND REFUSE TO PAY THE AMOUNT OF MY BILL AS IT WAS COMPLETELY UNAUTHORISED.FURTHER ,THE SERVICE THAT WAS RECEIVED FROM CELL C WAS UNACCEPTABLE