Is this a Breech of Rental Agreement?

We moved in and paid a certain amount & they were giving us a credit which is specified in our lease to be prorated through our entire lease. One day my husband went to pay rent & the leasing agent told him we actually have a two hundred dollar credit in our lease. That when we moved in we over paid and they owed us money. That we could use it toward our rent. My husband already had the rent check and told them we will just use it the next month. He told me about it and I told him to make sure it wasnt a mistake. Next month comes and they said Yes we only owe 700 because we paid 200 to much. Come to find out it was our prorated rent and now our rent jumped up 60 dollars a month they made the mistake and now expect us to pay for it when we don't have the money & put it towards other bills