Of course you should go down the legal route, but personally, if I were in your boots, I'd do what a friend did and change the locks and remove his possessions to a place of safe storage.
When he turns up, allow him access to his possessions, but not let him access to the property.
My mate did this and told his tenant to sue him. He never heard any more, and the tenant probably went on to rip somebody else off.
This is your property and he is taking the rise out of you.