Invalid Contract

I took a contract with vodacom last Feb 2014, my monthly debt order is R278 every month as i have capped the contract. This morning Vodacom debt me R310.00 so i call to find out why. i got told that the conditions of my contract have been changed and its going to cost more now. I am shocked that a contract signed by me for 24 months can change over night because Vodacom believe they should charge more for this?? Well Vodacom this means one thing.. the contract i did sign is now invalid and the current one of R310 is not something i signed for. I guess you need to come pick up your phone and cancel the contract.<br>