MTN will never see me again

My data bundle for my tablet was a signed agreed fixed contract. But my data bundle increased with a Thousand RAND, without my knowledge, consent, or any agreement. I just saw the amount debited from my Bank account. HOW IS THIS POSSIBLE. THIS IS *****... !!!!!!! MTN Three Rivers cant help me, MTN Head office cant tell me who did it, and I NEED TO PAY. I DONT THINK SO. I phoned 4 times, i stopped my contract, I reported it, and still you go and debit money from my account. Really this is not a service that i will use ever. please cancel my contract which I cancelled already as it has expired already, and stop taking my money.

What Else do I need to do. Take you to court?