Sounds like you went way over on your minutes or data (if you have a data plan) or you made international calls.
Have you registered for Self Serve? You can check your usage, see your bill and why you went over, etc. If you have, then log in, hit the Billing tab, select the most current bill, and go to page 3. It will show you the details of what happened (overages, etc.)
Evenings/weekends calling ends at 8AM on all plans.