thats unfair business practices, I thought the OWNER gave you the contract, the front office people work for HIM not the other way around.
You are contracting separately, under the correct and applicable laws. They don't have to pay you those hours, because you have your own equipment, truck etc.
So his thing he thinks he found is irrelevant. Who cares what the "front office" wants, you have a deal with the OWNER, exercise that deal.