Debit order problem

My name is Sizakele Elsie Nkonde My email address *** My ID no - *** I'm having a contract with Telkom for data since October 2020. I joined when they had the promotional deal of 80GB per month. We agreed that i don't want to pay more than R200 per month and my request was that should i exhaust all my data before month end they should cut off until the beginning of next month but they don't do that. I'm being debited almost R600 every month and I don't want that on this contract. I have called them several times concerning this issue, they promise to resolve it but they fail. I don't want to terminate the contract but I want them to stick on what we agreed on. Kindly assist me in this regard. Thank you Sizakele Elsie Nkonde.