Mtn refuses to cancel contract

I wouldn't say MTN is all bad, but try and cancel a contract...

I emailed customer service notifying them a month in advance that I would like to cancel my contract 31 March. I got a reply saying because it is a month to month contract, I can take the router to the closest mtn store and cancel on 31 March.

Which I did and got told I owe mtn nothing. So I stopped the debit order on the bank and went on with my life.

April comes, I get a notification that my debit order bounced. I call the branch who "canceled" my contract and they told me to come in. I went in and got told the lady who helped is not in and she would phone me the day after. So after wasting my time and petrol I went back to work, irritated of course... 2 days later I got a call from the lady at the queenswood branch to tell me there was a glitch and the contract is not canceled.

I asked her to please ensure it's canceled and to please sort out the outstanding money mtn thinks I owe them. She rep**** "no, you need to phone customer service and do that". Of course I was not very impressed as this was not my mistake and told her that she needs to sort it out. She flat out refused and said phone customer service.

Ok, so I try to phone customer service, and of course don't get to speak to a human. Eventually I emailed customer service requesting that someone phone me. 2 days later I get a call explaining the situation and get told that it will be sorted out.

Now, end of April, I get a notification that my debit order will go of at a certain date.

The contract is still not canceled and my credit score is going for a ball of ....

What else must I do from my side to get this contract canceled and get mtn to stop mtn from trying to get money from me that I don't owe them? I did everything they said I must do.