Sorry that you are experiencing such unprofessional behavior from your Realtor. Unless he/she is the managing broker for the agency you hired to list your home, you should definately contact the broker and insist that your personal items be returned to you immediately.
If that does not work, have your home rekeyed. That would be the safest bet at this point, regardless if you get your key back or not. Good luck to you.
Diane Wheatley, Broker