Unauthorized billing

I am on a monthly prepaid billing account and my average usage is R400 to R500 per month with a limit of R100 add on per month. I am on a Mtn 200 billing deal and purchase data as and when required. On the 1st September I ran out of data time and the call centre would not help me ( an extremely rude operator) and I physically went in to the Mtn office in Langebaan and purchased, on my Mtn account, a 2 GB top up for R160. And I was back on line. When I checked my balances at the beginning of October I was shocked to see that my account is R4557.16 for October which is 10 times my monthly average.<br> I have reported this wih Thembehle on the 8 October 2015 and was given a reference Req*** and to date have heard nothing. I have advised my bank to stop payment and have closed my account with Mtn and migrated to pay as you go. I have not requested and or bought any more data time since the 1 September 2015. And simply cannot understand how data time can be billed to one's account without approval of the account holder.? I have no contract with Mtn other than my monthly billing. <br> I get no response and do not intend paying this account until we resolve this issue.<br> Over to you Mtn!,