My son was turning left on a green arrow when a truck driving straight in the opposite direction hit him on the right corner of his car.

Who should be at fault? The person that hit him filed a claim with my son''s insurance company and won his claim. My son''s insurance found my son 80% at fault. There was no police report that was filed because both cars were drivable. The police were called because the other drive did not want to give my son his insurance information. The person who hit my son said that my son ran a red light but my son says that he had a green arrow to turn. My son had first called his insurance company to let him know about the accident but was told that he (himself) should have filed a claim with the other driver''s insurance. We are not sure if we should try to get a lawyer to look into the accident.