I would just call them and explain the situation and why you think an error has been made. I once got a parking ticket for my father, five years after he had died. Plate number was his at one time but the car no longer even existed. Called Newark, NJ and straightened it out over the phone and had them mail me a letter for my records that it was an error. If they won't handle it over the phone, a statement from your boss that you were at work that day, plus your and/or other's statements that you had possession of your car that day in LA should be reasonable enough proof your car was not there.

