Account cancelled, Credit score dropped due it showing missed payments...serioise matter this.

Last year October 2020 I canceled my Telkom services through the Telkom app. The call centre called me to tell me i had outstanding payments. I informed them that i have cancelled the account. I am not on a contract but month to month.

In early Jan i received a SMS to say my case no *** is resolved.

Now when i viewed my credit report my credit score dropped. When i investigated it shows that i have outstanding payments due on Telkom.

Below is the report. We can see that you've had multiple missed payments on your accounts over the past year.

TELKOM NGN 1st Nov 2020 TELKOM NGN 1st Dec 2020 TELKOM NGN 1st Jan 2021 TELKOM NGN 1st Feb 2021

Now i want to know why is this the case that is reflecting on my credit report? Secondly, i want this resolved at the credit bureau and removed otherwise I will take this further.