MTN Not correcting my Account

When upgrading my contract last year September I added a 2GB package to my contract.. . After many complaints it was discovered that the 2GB package had not been activated properly on my account and was stuck on the backend. This has now been resolved in terms of me getting the right data However my billing has still not been sorted . I have been overcharged an amount in excess of R6000 rand and MTN have only credited 3800 as instead of going to back to the date the problem started MTN only went back six months. I have queried this a number of times just to get the first credit and now I must fight for the rest, MTN messed up here not me so why am I the one footing the bill. This is totally unacceptable. I tried to log a complaint on their complaints page on their website but that does not even work?? I have again raised this issue today under Req No ***.