signed 1 year lease,paid= then 17 hours later I asked to cancel. There was a 250. Default charge, butt they want me to pay one month rent too. Can they do that

What exactly does the lease say about cancellation? When were you supposed to move in?

Where is this located? In most cases they can require you to pay until a new tenant is found. This makes the landlord whole. He does not loose money because you changed your mind about living there.