Data Theft

I recently upgraded to a new contract that included 5gigs of data...this was done as I had called their cancellation department and was asked why I was ending my contract with them. I told them that i wanted to change to Telkom as they had a contract that suited my needs in that I needed 5 gig of data a month. They decided to match telkoms offer and everything was fine for 2 months. The following month I had to spend over R800 extra in data and I could not understand why. The following month...on the 1st November...I checked my data balance and realized I was not receiving the 5 gigs as agreed. I tried for 3 days to make contact with their call centre and just got disconnected. I then went into one of their stores where I was told that they could not help me as the online division of Vodacom is a separate entity and has nothing to do with them. I then begged and pleaded(demanded) someone assist me and one of the assistants called the online vodacom line and tried to sort it out...there was some technical issue and they would reinstate my 5 gigs of data. When I asked what happens to the 5 gigs that I did not get the previous month and the R800 extra I had spent to get data...I was told there was nothing they could do. This is shocking service and theft as the 5 gigs is part of my monthly package...what can I do? So tired of been taken for a ride....