Air Bag Light On problems of the 1999 Mercury Sable

Started from a stopped position and heard a loud bang from under the car. Looked under the car to see if I had hit something. Nothing in sight. As I drove home, I noticed the car pulled to the rightand the air bag light blinked. Dealer investigated and stated that I must have hit something very hard because the sub frame assembly and passenger lower control arm were bent. I am the only driver and have never hit anything. Repair charge was $2056.