Mtn refuses to cancel contract

I cancelled my contract in November at the branch and went in again in January as the payment went off after I cancelled.

I've spoken to people on the phone and the branch again and nothing is being done. Mtn keeps *****ing my money every month and refuses to cancel my contract. Surely this is ********? Even after speaking to somebody at head office and after they promised me it will be sorted its still not! Haven't had a call back in months.