Unfair practice/overcharged/debit order

I took a data contract with Cell C in April for the amount of R199 p/m. This included 5GB daily and 15 GB night data. I took out this contract with the call centre where I specifically stated that I do not want an open account but to be able to recharge if the data should run out. I was insured that this was in order and that I will also be given a \pro rata"amount of data for the rest of the month as soon as it is activated. After a huge struggle to get this delivered I activated it. I was told the pro rata is calculated by the days left in the month"