Breach of Contract & Malpractice

I have had a Cell C contract for 24 months, recently asked if I want to keep the contract and I opted for cancellation & a R250 monthly bill went up R430 because I wasn't given a discount I received for 23 months, how's this fair? I signed a R250 24 months contract which entitled me to the discount - why is it stripped when I decide not to keep the contract? this is a breach of our contract and I am really disappointed with Cell C - do you normally rip people off like this or its just me?