How can i get my car daughters back from a shop

My daughters car needed a new engine, for months ago she took car to shop. she paid $850 for the engine and has since paid $470 on the $850 due for labor. He agreed she could make payments on remainder. Work has not been done and he refuses to give us car or engine we paid for. My daughter threatened to call cops and he told her go ahead, its a civil matter and they wont do anything. (He was correct, cops wont do anything) I am totally at loss as to what to do.