Standard Bank - Cause for poor credit rating

In July 2016, I closed 3 credit card accounts. The account with two other banks have been closed. From the start I found it difficult to close the Standard Bank account. It became apparent that the problem was related to insurance on the account. I eventually requested that the insurance be cancelled. However, to my total embarrassment, I just realized that the insurance was never cancelled and it was still debited to the credit card account. When I app**** for a Wi-Fi facility at Cell C, I was informed that I had an account in arrears, which ended up being the Standard Bank credit card (Blue Bean). The amount outstanding / "written off" is R1 034.00. I have never had any correspondence or any other form of contact from Standard Bank to inform me that there is a debit balance on the account. Not only am I embarrassed, I have also missed out on the Wi-Fi offer at Cell C. I called Standard Bank yesterday and I was informed that I will receive a sms with a reference number yesterday, which has not happened as yet. I am not able to provide copies of my e-mails, as my PC and other documentation was destroyed in a fire. Even with this negative note on my credit rating, I still had a score of 844, which is considered a low risk. How can this negative credit entry be rectified?