Auto Insurance Claims: Wrongful denial of auto claim, wrongful denial, certified mail

Question
My sons friend had an accident with his car. My son told his friend that night that he did not want his friend to drive his car because he had been drinking but his friend jumped in the parked car (the keys were already in the ignition) and backed it up with the door open in back. The door caught on another car and was severely damaged. I made a claim with my sons friends insurance company who are now denying the claim stating my sons friend had implied permission to drive the car because he had drive my sons old clunker before and had driven this car down the street once when my son first bought the car(my son wanted him to see how the car handled, my son was in the car with him.) Is it still implied permission even if my son told him that night he did not want him to drive the car?

Answer
The implied permission is not valid if your son had explicitly forbid his friend from driving his car. Have your son send a letter by certified mail to the claims office of his friend's insurer stating the facts of this accident and expressing his spoken wishes to their insured.