ABSA has no control over the debt collectors they contract to.

I had an outstanding debt with ABSA which I settled through a 3rd party in May 2022, since then I have been harassed by a separate company, MDB for an amount that was discounted by the first company.

Even after sending the paid-up letter MDB keeps calling me on behalf of ABSA and threatening me with legal action OR just hanging up the phone OR just ignoring my emails.

Surely after presenting the paid-up letter, this should stop, surely ABSA has a control in place to stop debt collectors from harassing people after they have settled the account?