CONTRACT CANCELLED BUT STILL TAKING MY MONEY

In December 2016 i called the call centre to cancel my contract, which was expiring, i was told it will be cancelled. Then i noticed i have been billed and they have deducted money from my bank account, then again on the 06 January 2016 i called and spoke to a lady named Thandeka and cancelled again and told her that it should be cancelled with immediate effect. I have realised that MTN is still deducting money from my bank account and i am not even receiving airtime anymore. I have had endless problems with MTN and that is the reason i did not want to take another contract with them, we sign a 24 month contract with a set amount for 24 months but they still increase it. REALLY PATHETIC SERVICE AS WELL FROM THE CALL CENTRE . THEY DO NOT HELP AT ALL. I would like MTN to refund my money that they debited for the last three months.