MTN complaint: Uncancelled contract

I had a contract with Mtn. Sometime last year, in November I missed payments, and then Jan this year they sent me a final notice letter requesting I pay an amount of R3400 and stating they are canceling my contract. I then went ahead and paid the R3400 requested since it included early cancellation. After the payments, I went ahead via email to notify them that I’d made the payment and both customer service and retentions replied to my emails requesting all the necessary information. The contracts were ending in April and May and I told them to go ahead and cancel the contracts as per the letter stated since I was unable to make payments. The monthly payments were around R551. After making the payment of R3400 as requested and giving them the go-ahead for the contract they did not cancel. After April they moved my contract to prepaid even though I told them to cancel my contract and now charging me R340 every month for data. I refused to pay that money because I requested my contract to be canceled and I was not making use of that service. They now took my account for collection even though I’ve called and tried to dispute this whole thing and sent them emails as proof that I did request cancellation.