Impossible to cancel contracts and ask for paid up letters from MTN

I have now had it with MTN, I would never in my life have a contract with your network again. During 2020 MTN listed me as a default payer, I then communicated with them and paid the outstanding amount of R135.33. They confirmed receiving the money, I have since 2020 requested a paid up letter from MTN, but have not received any communication from then. Some of the correspondence took over a month from them.

Over the last year more than 1 debt collecting company have contacted me informing me that I now owe MTN R650.33, i have not received any correspondence from MTN nor the previous debt collector Saya Recoveries up to date! And today i get another call from a different debt collector.

Can someone please sort this out.