As someone already stated- unless they have valid reason for with-holding the horse you can contact the sheriffs dep't of the county they are in and get it taken care of. You won't necessarily have to hire lawyer and go to court etc. If you give the sheriff's dep't proof that the horse if yours, they will go and handle the matter. Most people will back down if the police become involved- especially if they are brought to realize they are in the wrong in the eyes of the law. I would take it step by step and if the sheriffs dep't attempts to blow you off, bring up the very valid point that you are reporting a criminal action and they are obligated to assisst you.
Basically long story short a verbal agreement made was broken. Horse is stuck in NC with unwilling relative while owners live in NJ. Owners have proper documentation of ownership that AHA registry & nj state labs are aware of. NJ & NC horse council have been contacted with little help available. We do not have the cash to hire a lawyer, relative has been holding him since January. 11 year old girl is heartbroken, please help with any advice.
You're going to have to find a way in that are and get their advice then find a trailer and go down there yourself WITH law enforcement and proper documentation and pick the horse up.
Just wanted to add something. Just go take a look at the other thread I just posted about the lack of payment and boarding, don't remember what the thread was called. Lots of great advice there that will work in your situation.