Vodacom billing increase

I received a text message from Vodacom at the beginning of April saying that my data allocation and pricing would be going up. Firstly, most of the customer care agents I have spoken to have tried to convince me that this increase is due to VAT??!! It clearly isn't, I have then been referred to the terms and conditions of the contract saying that Vodacom reserves the right to change the contract and billing. I have a huge problem with this. I have budgeted a certain amount for my contract for two years, I did not account for any increases. They told me that no one else has complained so I will have to accept this extra amount or terminate the contract, and since it is very new I will have to pay a large penalty for cancellation. I think that this is completely unacceptable.