MTN does not take customers seriously - contract cancellation

I have been with MTN for years, had contracts with them since 2012. This year in March I called to cancel my contract and I was told the cancelation was being processed I need to give last payment of R299 on the 20th of March which I did.

This month April 20th I get a debit order of R1700 from MTN which I did not understand what it was for. When I call they told me i never put in a cancelation of the contract so I got billed on normal prices, luckily I had an email from the consultant who assisted me the day I called for cancelation. When I forward them the email then they say its a system issue cancelation was not processed. Fine I understand that, so I need a refund of R1700 because thats way too much from the R299 I was paying every month. I logged a query for a refund on the 21st of April and haven't heard anything from MTM since, today I call to follow up I keep getting transferred from one department to the other.

I am frustrated as I did not plan to get a debit of R1700 in my account. This is messing up with my budget. I didn't want to reverse the debit order as it might go off again next month in May.

I am very disappointed in MTN with this incident how can they bill me 5 times more than what I used to pay for a canceled contract and delay to refund me when they have said its their system error?