Payment not reflecting on account

On 30 January 2015, I paid my Edgars account in store in Tygervalley. During February, I received a phone call asking when I am going to pay my account. I told them that I paid it and the next day I went to the bank to obtain a bank statement. I went to Edgars with the bank statement and expain my problem to Bongi who is working there. She made a copy of my bankstatement and faxed it to their helpdesk for assistance. On 17 February 2015, I went to the store again and told them that my account still does not reflect my payment and I see that I was charged interest for non payment. Again Bongi assisted me and again faxed the copy of my bankstatement as proof of payment to their helpdesk. Up until today it is not rectified and nobody phoned me with regard to this matter. This is very bad service that I get and being charge interest on my account that is paid, is totally unacceptable. What happens to my credit rating because of them?