Air Bag Not Deploy problems of the 2009 Ford Flex

My Flex started having a hard jerk and bang when going from reverse to park. Was not always but frequent. The car started to run hot when sitting in a drive thru or traffic but would go right back down when I started moving. I took it into s mechanic and he replaced the fan. After replacing the fan the car began to have a really bad grinding noise when idling or traveling. Do bad I did not want to drive it. I took it into the Ford dealership and after 2 days they call and say they can't find anything wrong. Within 4 minutes I get another call daying I need a new transmission. The car would eccellerate on its own, shut off intermittently, and car would lag between 3rd and 4th gears. Ford dealership advised me to have a knew transmission put in. Car will shift properly most of the time even on highway. Only get whining noise at low speeds. I was also in an accident causing $13000. 00 worth of damage to front end and airbags did not deploy after hitting a car doing 35 mph.