The accident while not having the seatbelts

As I was one week after the surgery (I had my appendix  cut out) it was painful to put the seatbelts. I had to drive my children to school so that I had to use the car. Unfortunately, it was slippy on the road and the other driver (another mother who was driving her kids to school) didn't manage to pull over the car and she hit my vehicle. The insurer denied to give me any compensation saying that it was not serious accident and that I had no seatbelts which indirectly caused the injury (I had te fracture of my nose). In fact due to the accident I had to go back to the hospital and the doctors wanted to operate me one more time as there was some small bleeding.. Is it possible to put all blame on me? How should I defend myself?