Vodacom the *****'s

I been a loyal client with Vodacom for 5 years I have a contract where I recieve airtime off 175 I use it to by data I notice I'm been charged a higher rate for data so I purchased 1 gig of data for 150 I managed to save my data until the end off the month so it can roll over and I don't have to buy more data however on the first I notice my data have been finsh when I call vodacom they tell me the data have and expiry date but it's my data I bought that really unfair