Sounds like the airport, county, or prepaid parking have nothing to do with the situation. Sounds like you were involuntarily denied boarding due to an overweight situation. I'm sure more informed flyertalkers will have some information on the IDB compensation required by law. Your issue is with Delta/Comair. I would make sure to use the words "involuntary denied boarding" in your discussion.

I do agree that dealing with undertrained contractors can be a pain.