Raising contract amount without my permission

I am one of the unhappy vodacom clients that received an email saying that my contract amount will increase.<br> I am quite sure that the contract I signed has a part that allows vodacom to increase the amount without my consent, but I still feel it is a breach of contract as I had no choice in the matter. I can not not have a cellphone/data contract therefore I must sign the contract. Stopping the debit order will only start a fight that a small individual can not win against a very large company such as vodacom.