Data never received eventho its part of phone deal

I purchased a cell c jewel prepaid package from cell c westgate mall branch cape town. For the past 3 months I have had to physically go into the store for the added benefits of 1GB data which the deal included. Today expecting my data I again was forced to leave what I needed to do to go to the store only to be told that I now have to buy a minimum of R50 airtime to get my promised data which was never explained when I bought the phone. It was also not on any of the advertising materials on the phone at the time of purchase. Cell c s refusing to keep their side of our purchase contract and I keep loosing work time and petrol having to drop everything to go into their store to get what was agreed on at the time of purchase. Why do big business get away with changing purchase terms and the little guy foots the bill.