Nu Debt and Telkom stuff up

I had a telkom account which was paid ahead. I closed the account and they owed me just over R2000. They kept billing me incorrect amounts, eventually I got them to acknowledge that they in fact owed me money, and they paid the money due to me in July 2019. I started getting harrassed by debt collectors for the money Telkom still thought I owed. Ridiculous. I send numerous proof of the money having been paid back to me by Telkom but the debt collection sms's still kept coming. I eventually send Nu Debt a desperate note to please stop harrassing me and resolve this with their client. They eventually did. However they did not get my name cleared so now until 2023 I am marked on my credit rating as having missed payments for 5 years !!! So what now ????? Nu Debt should not allow this. Who placed this mark against me ?? It needs to be retracted as it was proven I was not at fault but between Telkom and Nu Debt they have been able to ***** me over. Well done.