I have been having MTN cell phone contracts for + - 20 years , but when I canceled their contract to prepaid , I recently found out they've taken my name to Credit Bureau for R114 they say I owe them which they didn't notify me, well I paid

I have been having MTN cell phone contracts for + - 20 years , but when I canceled their contract to prepaid , I recently found out they've taken my name to Credit Bureau for R114 they say I owe them which they didn't notify me, well I paid the money in July but now they don't remove my name from blacklisting which gives me a bad credit score. Thank you 🙏