Price increase

Vodacom Sent me an email today informing me that my contract package is one of those that will be affected by a price increase as from May 1,2015. I feel I'm being shortchanged since a signed a 24 month contract based on the figures I was presented with at the time. I thought being in a contract protected me since we agreed on the figures. If I wanted a higher subscription then I would have signed for one, but instead I signed for one that met my affordability. I'm of the opinion that my contact should be left to run out on what I've signed for. They should look at new contracts and rework their fees. Or I should be afforded an opportunity to get out of the contract. I find the whole thing unfair and uncalled for. We are carrying the increases left, right and center without any choice/say in the matter.