How can my rates go up if I signed a contract for

How can my rates go up if I signed a contract for 24 Months. On top of this if you want to cancel your contract you have to pay penalty fees ? How is the consumer protected here in any way ??<br> <br> Surely you can only increase prices on new contracts nor existing contracts.<br> <br> I'm disgusted Vodacom !<br> <br> South Africa's cellular rates are of the highest in the world, it's really disgusting !