Disappointed client

I had a load with Unifi, and they handed me over to GL attorneys, and I paid all the money they said I was owing, R11 600. Now I got messages from other debt collectors, they said I was handed over again by UNIFI to them. UNIFI never sent me a paid-up letter since January. I tried to call their office, and they promised to call me back by today. I really need this issue to be resolved because the other debt collectors are harassing me.