MTN - How can we make u miserable

I canceled a month to month contract on the 6 th of August. On the 31st July I handed in the device where I bought it. I was debited til Dec for that contract. Whenever I called I was told it was canceled or the ticket is in progress. I ended up having to go to their head office in Roodeport to get the cancellation done. The sad part is this has affected my credit score, MTN reported missed payments n what was I supposed to pay for because I had handed in the device. Now that I want to fix my score, they can't even send me a cancelation letter, I have been requesting a cancelation letter n they reply with a 1 sentence email. How pathetic