MTN charges me for services I don't have

We received a statement from MTN in mid Feb which included charges that were not for our cell number. This was queried with the branch at Cresta and we were told that this new service on our account does not exist and not to worry. I also wrote to customer care who rep**** "Kindly be advised that the line has been deactivated.". I then asked them what this meant and they rep**** that it had been escalated to the ***** department. I phoned MTN on 17 Mar as I was still not convinced that this had been dealt with and they escalated this issue to the billing department. The debit order has gone through today and we have been charged over 10 times our normal bill for a service we know nothing about. Also, MTN has done nothing about it and it is impossible to speak to anyone who can help.