car insurance emergence

My friend's car was totaled in a car accidence recently when his wife drove it. The driver is ok. The problem is he can not show evidence that his wife's name has been added to the driver list on the insurance. He remeber that he did add his wife 's name on it and received a notice. However the insurance company forget to do it later on. He did not pay attention to it and can not find the notice until now. Now the insurance company refuse to pay the loss . What can he do? The car is just 3 years old and it is a big loss for them. As I know it would not cost anything to add family name on the insurance. Does anybody have good ideas on this. How can he argue with the insurance company. Is there any way to get the money back ? Is it helpful to hire a lawyer? You help would be highly appreciated. Thanks a lot in advance !