heating oil company fill up the tank after we told them not to

Petro, a heating oil company filled up my heating oil tank after we called them not to do that, because we don't need a full tank of the oil for rest of the winter.

They ignore what we requested. The contract will be ended at the end of the Feb.2010. The want to fill up the last tank to make money.

Anyone knows how to deal with it.

Thanks,

-Lisa