MTN and their false contracts

I have been struggling for two months to cancel a contract upgrade with MTN which I never asked for in the first place. I never signed, paid or received a notification of this upgrade, until two months ago when they wanted to bill be to the tune of R8000. Since then I have been in constant communication with MTN's outlet in Potchefstroom, who have supposedly been contacting their head office. So far I have yet to even receive a reference number. I would very much like to settle this matter, but find that MTN's customer service is severely lacking. Any help or advice in this regard would be very much appreciated!