Can companies fill your propane tanks without permission? Now I have an unscheduled $303 bill!?

A local company filled our propane tank without us asking. They don't own the tank & we don't have a contract with them. In fact, this is the 2nd time they've done this. How can they get away with this stuff??? I called last year and told them we would call them if we wanted it filled and they said they would move us to a "will call" list. Propane is now $3 a gallon. They seem to do this when propane is at its peak! I may have filled it at some point this month, but with spring around the corner, i would have only filled a quarter or half the tank at the most and then filled it later when the prices settle down after winter. What should I do? Refuse to pay? Tell them to come get their gas? Suck it up and pay? Offer to pay the wholesale price?