Report them to THS. Use the words «member dispute» as that is the phrase that will trigger THS to start an investigation.
I am a sitter myself, I don’t want members like that on this platform. That’s blackmail in my book.
If you don’t get good applicants, an option if you wish to do so is to link your listing to your forum profile and start a topic where we can help out and see if something could strengthen your listing, and get better matches for your sit.