Overcharged by Double for the last 4 months

I am on an MTN 750 Contract, which allows me pus/minus 500 minutes airtime per month.<br> I have been on this contract for 18 months already, and my bill has been constant at R 1090.00 per month on Debit Order. <br> From May of this year till August my Bill has more or less Doubled per month.<br> I have done a recon. on my account, and have never exceeded 500 minutes per month. However, from the recon I have noticed that from May this year, I am being billed after using only 200 to 300 minutes, which is not as per my MTN 750 contract so in fact being charged Double.<br> I visited 45 Days ago, and reported this twice, to the Accounts Dept. in 14 Street. After numerous phone calls with no joy, on my second visit, the person responsible admitted that there was a problem and that I was out of pocket for<br> R 3,500.00. To date nothing has transpired, and I have not been re-funded.<br> Regards Gideon Lapidus