CANCELED CONTRACT SHOWING STILL OWING

I called MTN to cancel my contract on the 3rd January 2023 and asked how much I needed to pay, went and paid that amount on the 4th called again to let them know I paid on the 5th so they can now cancel and send me proof that contract is canceled. I was told it's canceled and was given a reference number instead of proof of cancelation when I asked about it. From March 2023 MTN has been saying I'm in areas of from R1100, it keeps going up every month by less than 20 rands and I've been calling being sent from pillar to post, sending emails with no constructive feedback as the emails I get back look computer generated. I tried going to MTN thinking head office would help since I tried going several MTN shops but was basically told they are just the same as the other shops and they can't help but also send an email to retention and I eventually get an automated email saying my case has been closed but with no solution

This is really affecting my credit as it appears as an unpaid debt every month, it is weighing me down