cancelling a vs contract

I tried cancelling my T-Mobile contract after the whole Night minutes promotion every other provider ran. But was advised that the Unlimited nights promotion will hit all T-Mobile markets late september. Subsequently, plans they said will also be tailored for daytime users as well as nightime users etc etc and terms of all contracts will change. You can use that clause to get out.

My advise stay with them, among all the evils out there, they seem to be the best.