Constantly harassed for payment on a PAID UP account

In December 2019, MacRoberts Attorneys, on behalf of Standard Bank, offered me a settlement amount which I accepted, paid and received a paid up letter for. I am now being harassed on a daily basis by Standard Bank saying that I still owe approx. R6,000.00 on this account. I have been pushed from pillar to post by Standard Bank and MacRoberts have told me they have escalated it to Standard Bank however day after day I am being harassed with no-one willing or able to resolve. I have provided the paid up letter numerous times to numerous people. I have been in contact with the NCR and am in the process of lodging an official complaint against Standard Bank and MacRoberts.