Hey Amy,
Sorry to hear of the trouble you're having. As the yard is not answering your telephone calls, have you tried calling with your number set to private? (most mobiles have the option of not sending the mobile number).
If you have and still no joy I would be contacting your local police station and if you can get them to even take your report, I would report it stolen.
By the way, what on earth were they fixing for you to have required your car overnight anyway??
Best of luck,
Karen