Paid Up MTN Contract on credit bureau after a year of settling it

I had a contract with MTN few years ago and when I noticed that the monthly payment did not go off, I went to MTN (St Georges Mall) which later closed with the hope of renewing my contract and get a new phone. The consultants told me that they could not find my number on their system and confirmed that they do not see any amount owing. A year later, I found out on my credit report that I am owing MTN R 900.I then went to MTN (Waterfront), Cape Town to settle the outstanding balance (a year ago). I was then told to contact MTN Customer line for a paid-up letter and request them to update my account with credit bureau. I have been transferred to different departments for a paid-up letter ever since. I ended up sending a complaint through complaints management and received hope that the credit bureau has been instructed to update my account. I have not received the paid-up letter until today. I have been sending follow up emails every week. I was also told that nothing can be done to follow up with credit bureau. This has negatively impacted me (lost opportunities because of this).MTN branches do not assist customers instead you must call the 135 number. You wait for more than 30 min to get someone that will transfer you to someone else.