Which lien holder permit me to move my car overseas?

I'm a military and have order to Germany and I need move my car to Germany.I live in USA now. The problem is that my lien holder don't give me the letter that can permit me to move my car. So I have to pay the remain total, like 6 months payment $1,800 is to much for me or sell my car before left. This is a bad experience for me. So next time I want to make sure how to do business with my other cars in the future. What can I do?