Prodigy marine

These guys are crooks - beware of them!! They've got our boat since last year, and just won't give it back to us. All the repairs have supposedly been completed, and we've paid all the invoices that were sent to us, but they keep making excuses on why they can't give our boat back. At this point, they won't even return our calls!! We're concerned that they might have sold off our boat and pocketed the money. At this point we're not sure whether we should go to the police or hire a lawyer. Any suggestions on how to recover our boat would be much appreciated.