MTN CLOSED ACCOUNT - BAD CREDIT SCORE

I closed a contract account in 2020 and it was not in arrears but MTN never updated their information because later that year I started getting calls from SSDA saying I’m owing MTN I don’t know how many times I’ve told Shapiro shaik (SSDA) that I don’t have an MTN account anymore even to date I still get calls and SMS’s and recently I checked my credit report and it shows as I’m Owing MTN still now I have a bad credit record for something which I paid up a year ago!