Bad service

My unisa account fees has been handed over to Hahn collection. I have paid all the amount I was owing and I have send an email with all the supporting documents to your company and unisa finance.

I keep on receiving sms' almost everyday saying that I owe while I paid all the amount I was owning.

In addition to that, I call almost everyday to try and solve this matter but no one seems to care.

Could I kindly please get assistance as to where can one escalate this matter to or report it to?