Blacklisted for a debt that I settled!!

This company has given me grief over a debt I settled in September. I have been calling them since September of last asking them for a paid up letter. They never get back to me or I end up being played for an idiot by supervisors I don't even believe are real supervisors. In December I requested to speak to someone incharge and I spoke to a lady who's email address is ********** she told me to send her my proof of payment which I did and I told her I'd call back immediately but she was on "lunch break" then I spoke to the supervisor who was on the floor at that time ********** who asked me to do the same thing Nomsa asked me to do, which I did. Later I called to ask if he received my email and he was apparently on "lunch break". I haven't been able to talk either of the supervisors till today. I later called and spoke to (I'm assuming) consultants who have been either hanging up on me or simply telling me something new every single time. I have recently been told to send my proof of payment to the enquiries department which was supposed to get back to me but hasn't. I tried everything to clear my name from this debt but nothing has worked. I even went to as far as going back to the store where I paid my balance but the manager couldn't assist me. I am very angry and would like assistance with this company and unregistering my name as a bad payer for a debt I settled.