Disgruntled client

I had a cellphone contract with MTN that ended in November 2021. I called in to have it cancelled. But recently its reflecting under my credit score that I am in arrears with mtn for an amount of R4.11. I have been talking to mtn agents since 8am today and still no resolution and am being sent back and forth between departments. I have spoken to retentions which has advised that my contract is cancelled and I spoke to billing as well and they advised this is because when my contract with cancelled it wasnt cancelled properly local voice was left with amounted to the R4,11. So now I need this cleared and also my credit to be rectified and not have this reflecting under my credit as this is not my fault. I need this cleared its affecting my credit.