data ripp- off

I bought 1 gig of data from Vodacom and I was just using it on Internet and emails, within a day it was finished and I hardly use the data, I bought another 2 gig today and it's already finished. I have a contract with Vodacom which gives me 2gig and I use that 2gig for the whole month sometimes it even overlaps how come the prepaid data dissappear in few hours? Something is not right here. When I call the call centre the idiot could not explain why. I need my money back.