Failed Cell C Contract Termination

It was December 2022 when my contract with cell c was about to expire and I decided to terminate it. Apparently I called them in mid-December that year and they told me that it was a short notice so I was suppose to wait till monthend for the last debit order to run. It happened that they took their money that monthend and got a message around mid-Jan 2023 that my contract has been terminated successfully. I was surprised when I started receiving endless calls around May 2023 from MBD debt collectors that my cell c account has been handed over to them due to a failure to make a final payment. I called cell c regarding the matter and they told me that I was supposed to pay a cancelation fee which I did not know nothing of and when I followed up with them again, another consultant told me that there was data and airtime loaded prior to my contract cancelation maybe that's what caused my account to be in errors which I was not even aware of because I removed the sim card from my phone as soon as I got a message that my contract was terminated. I then decided to pay the amount that MBD collectors requested me to pay in order to settle my account on the 2nd of August 2023, I sent them proof of payment and forwarded cell c, I have been calling to find out how far are they to close my case and give me a settlement letter but both cell c and MDB are failing to do so. They keep on calling me that my account is in errors and worst part the amount is increasing. I would really appreciate your efforts to help me to settle this matter by getting a settlement letter and that MBD clear my name on their list. Thank you in advance...