he has had the car for a month and wont answer phone calls can I take my car
See Minn. Stat. 514.18, which conditions the mechanics' lien on the performance of repairs "at the request of the owner or legal possessor" of the car.
A letter or call from an attorney probably would do the trick. If the police won't become involved, which they almost certainly won't, then you'd have to sue to get your car back.