Bad service that affected my credit score

i checked my credit score recently and found out that MTN claims i owe the R312 for a cancelled contract sim that was never used due to the MTN consultant that ordered a wrong contract option for me, i immediately terminated the sim without even using i single megabyte of internet and it was confirmed that i wont be charged a cent. today after picked up i have an account with them that was updated on the 31st october 2021. This is pure bad service that affected my credit record negatively.