Horrible service from mtn

MTN won't cancel my subscription. We never agreed on a debit of R400. I was told that R50 would be added to my contract ***. I have called them on countless occasions and I don't recieve any assistance instead every month they keep debiting an amount that is incorrect. I have told them on several occasions that if they cannot cancel this subscription they must just cancel my whole contract. I keep getting told that they are working on it but I never get a response from. They don't take me seriously