Insurance does not want to pay me the amount my car is worth afte rthey sateted the car is totaled. What should I do?

I was in an accident that was not my fault. My car was in the shop for three month for repairs, only to find out today that the insurance wants to TOTAL the car. Which is okay with me, but they are saying that the car is worth $12,000 and that the repairs were $8000, and that they are only going to give me $4000. HOW is this possible, I did not make that decision for the car to be rapaired then to be claimed TOTAL loss.

What should I do? Please help me.