Nimblepay and CellC bulls#&@!!!!!

This company must be a ****. They have harassed for long enough now. After settling the account and forwarding them the proof of payment multiple times, the default has still not been liftes as Cell C handed the account over to them. Terrible Service. I want to reverse the payment from my banking app, I don't know why CellC failed to make contact before even handing over this account. Im livid. How do I get this default lifted. The payment of R5000 was made to settle this account and to no avail, the default is still there and the amount due still reflects.