Change in the contract

I subscribed for 2GB data with Vodacom for R99 a month for 24 months, hardly two months after my upgrade i get an SMS stating that the subscription will increase to R109 per month from May 2015.<br> This is masepa ao nkekeng ka a dumela, ha ba lo nyela or cancel the contract because i cant afford the extra R10 that we didnt agree on.