I do not have any dealing with log book loans myself, my experience in borrowing is limited by cash loans online, but I have dealt with them on behalf of third parties. My advice would be to hide the car, state that you call the police and bring harassment charges, trespass and possible criminal damage. In one day I recieved over 4 calls and I was shouting at them not to pester my parents who did not have an account them. Another example of their behaviour would be to attend at my parents', late at night around 9pm with four men. This was frightening for my parents' in light of their age, and their rural enviroment.