Everyone here is taking Hertz and PlatePass's side. I can relate to the OP. He probably had a business meeting he had to get to Monday morning, hence he was renting Sunday night. With a long history of loyalty with Hertz, he expected to be able to rent a car. But no.

This is why we deal with both Hertz and Avis. If one of them doesn't have a car or won't rent to you, you can always rent from the other.

Although the OP states that this charge was legit, PlatePass has a history of double charging and over charging customers. They get little sympathy from me.