I've had that happen before. Not pretty. Call an equestrian association to get advice and support or a cycling association. At least they can back you up in pushing the police to lay charges.

You may want to try a technique used by cyclist. They carry a kryptonite lock in their hand and use it when a car deliberately tries to run them off the road. If the car causes them to fall the kryptonite conveniently goes threw their windshield or leaves one hell of dent on the hood. If you have lost your balance or are falling you can't control where the kryptonite lands. Hell, put a large rock in a bag and use it for self-protection. This guy is using a car as a weapon.