False promises and unanswered phones.

I have Been dealing with Sigma for just over a month... Trying to get a paid up letter from them. My direct axis account was handed over to them. I contacted them 2nd week of June and I was told I have an outstanding amount to pay. Without hesitation or statement I made the payment of R656.39 and faxed proof of payment. After paying I called again and I was told to wait 7 working days. After the 7 days I called almost everyday. Most days there is no answer and when I do get an answer I'm told the person dealing with my account is staring later on. I have really had it with... Their actions or rather non action has caused to be further stuck in debt review. I'm unable to get my clearance cert because of sigma I don't know what else to do?