24 month contract price increase

End of January I upgraded my phone and signed a contract for R219 x24 months. Yesterday I get an e-mail and sms from vodacom to say that from 1 May 2015, my contract monthly premium will increase. <br> <br> Firstly nowhere in my contract does it state that prices are subject to change, secondly if I sign a contract of R219 x24 months, it actually means you pay that amount for 24 months, DUH!!! <br> <br> What's the point of signing a contract if Vodacom is not going to adhere to it!!!!!<br> <br> Please respond as a matter of urgency or I will take this further!!!!!!<br> <br>