High Data Cost

I took out a data contract with MTN about eight years ago. I had a credit limit set on this account for R 1548.00. I was forced to use this card while on leave over December. I then got a bill for +/- R 1800.00 which I paid. The following month I got a bill for over R 5000.00 which I refused to pay and reversed the changes as I limit was supposed to have been set as indicated above. I was charged at a rate of R 1.67 per megabyte which was possibly the original cost of data eight years ago. The present costs of data is in the region of 2 cents per megabyte from Telcom My contract was never upgrated. I also asked them to close the account which they never did. MTN wound not give me a rebate as they said that my account was a vetted account and was thus not subject to a credit limit. Regards