I hate to see things like this in the hobby. There are some heartless
providers out there as well as mongers. I would expect this from a BP provider, but the rates you are stating, indicates she was upscale and DDG.
You had no obligation to give her anything for canceling with a 24 hour notice unless it's stated on her website. Your mistake was assuming she was going to make it up to you on your next visit. The agreement should of been made when she came to pick up the $600.
It's time to get over being pissed
and let this be a lesson learned. When dealing with a provider always be specific about what you want.
My ATF makes things pretty clear on her website. She not looking for a boyfriend. It may be pleasure on your part but it's business on her part to serve you the fantasy.