Unauthorised data bundles

For the past two months MTN have added R4000 on my monthly bill (which is on debit order *and* goes off before I get my statement). I have lodged an official complaint, have a case number which after a month has not been addressed, and now when we I call MTN I can't get through because after pushing '0' to talk to one of their "service champions", I get an automated message informing me that there is either no such number or I have not made a selection. Incompetence and theft. Would appreciate if you can assist, if I can not sort this out today I will be cancelling the debit order with immediate effect and porting my number to a service provider who actually provides service!