Cellc's mistake reflects on my credit score and no assistance given to rectify!!

Once again I have tried to solve this issue through all available methods of communication with Cellc themselves, but am forced to come to hello peter to try and get results. The email I sent to log my query (on the 9th Dec) remains unanswered except for confirmation of the receipt thereof.. Called their Customer care centre just now and ended up being transferred in circles between departments.. I eventually just hung up.

I had a dispute with Cellc about a penalty fee that was charged to one of my accounts earlier this year.. Months of correspondence, between Cellc and myself, went by with only frustration and them not listening to my problem. In the end I also wrote a review about it on hello peter and cellc finally listened and corrected the mistake. They apologized and removed the penalty fee from my account. Thought that was the end of it, but found out in the mean time that they reported the same penalty fee to the credit bureau and it was not removed. Now I am getting a negative effect on my credit score due to this penalty still reflecting on my name.. a Penalty which was a mistake from their side!? I am so frustrated with Cellc as I have had one problem after the other with them, with what seems like no way to solve anything due to incompetence from their customer service department.