INCREASE IN VODACOM CONTRACT

I received an email advising that data bundles which i signed a contract for 24months will increase from R99 to R109 as from the 1st May. i only signed a contract with them which started in February. i do not agree that they firstly did not know about the increase or that anywhere on my contract does it say subject to increases when they feel it necessary. I have not even enjoyed the benefit of paying R99 for a year and i have to pay more. they just assume we get increase at the same time they decided to put up their prices. that difference affects my budget and i did not agree to pay that amount. i have been trying to call *** with no reply to have my contract cancelled immediately. i only use vodacom for data and nothing else. i am not prepared to pay more when i have just started this contract with them.