Bad service

I have really had a very disgusting service with CellC, I had a mobile contract with them in 2018 and decided to settle my account as their service was awful. I settled my account prematurely in 2019, a few months after settling my account i decided to check my credit score report and found out that CellC says I owe them R100, I called them and provided all proof of payment, they then admitted that they are in the wrong and that they actually the ones who owe me R100, which they paid. They said they will make sure that my credit report is fixed with Credit Bureau- till today I am being sent from pillar to post and my credit report still shows that I owe CellC R100