Unsatisfactory service

On the 31st May 2015 a vehcile slamed into the back of our vechile on the M13 in KZN. I couldnt get the regastration no as the car just drove off. Now Outsurance wants our car to be written off as its to costly to be fixed. However I dont agree there is notthing else wrong on the car besides the damage of the accident. I can get my car fixed for less than what Outsurances choosen panelbeater can fix it for but Outsurance is only Paying out R12057 and its going to cost me R16 338. Why do I pay insurance every month if they dont want to pay out the amount that I need to get my only transportation fixed. All Im asking is to pay me out the R16338 to get my car fixed please as I dont have the money for another car payment nor do I have extra money laying around to pay in the difference, that is why Im paying Insurance in the first place. I don't see why must I be punished for someone else, this is totaly unexceptable. Pay me the amount needed to fix my car and thats all im asking.