Sprint - Sprintspcs bait and switch, over-billing Internet

We've been having billing issues for the past few years - we decided to drop Sprint since our contract was over. We called to cancel our account and the guy in charge of cancelling accounts listened to our reasons for dropping sprint and said that if we stayed on board - he would give us a discount that would bring the monthly price down dramatically.  We stayed on board because of this promise - and the first month the discounts were applied, but the following month they stopped.