Theft of services ... he allegedly agreed to pay them each US$500 for their services, then only paid them US$100 each.
There may also be cause for action in small claims court, for breach of contract.
It's not a criminal matter, of course, but the voters might want to know that their Senator is a skankburger.
Make that a cheap skankburger. I imagine if these people that frequent hookers in foreign countries paid enough, we’d never hear about these things.