INCREASE IN PRICE WITHOUT CORRESPONDENCE

I have had a contract with Vodacom since the inception of cell phones and for the first time ever, Vodacom decides that even though I agreed telephonically to a contract for a specific amount per month over 2 years, they just decided they would put that premium up. I never agreed to that and have never ever experienced anything like this. Then to be told that it is in the terms and conditions and that Vodacom internal and external lawyers have looked at it before decisions were made and they can legally do that. I cant change my subscription though or cancel or I will be sued. What type of business practice is this? Its not about the money, but the principal. I apparently was sent an email. Well I am still waiting to receive one. UNACCEPTABLE! Will certainly not renew a contract with Vodacom ever again as this goes against my principals.