refund request

In really upset, im being billed out of bundle data usage when i have a closed contract meaning i only get 100min 100mb they charged me R500 extra march another R 200 when i called them they promised the problem is resolved but its not. I spoke to a sup he told me the same story i need to wait its been over a month and nothing instead im still being over charged in going to give them chance till the end of the week April 24 then im going to speak to a manager and complain at the ICASA. Im tired of mtn