MTN hounding for payment ended contract

I have experienced the worst customer abuse from Mtn.

My contract ended with MTN in March.

Firstly they did not contact me to inform me and they continously kept deducting half of the money they debited for my contract.

I decided to be lenient and let the amounts which were deducted go. I then contacted MTN to cancel my contract and informed them to stop debting from my account. The next month they debited again, I then called again with the matter they said it will be cancelled. This month they are still debiting they are even sending me letters to pay. I have sent email after after still my matter is unresolved.

I am at my wits end this is customer abuse and I am highly frustrated.