If it is your own insurer (unlikely; in this situation, it's usually the insurer for the person who injured you), you could sue them for breach of contract--for not honoring their obligation to pay you what they were supposed to pay under the terms of your policy. You would need to show what they are supposed to pay under your policy and the extent of your injuries or disability.If it's the insurer for the person who injured you, you would sue that person (you sue them, not their insurer; the insurer does not owe an obligation to you, but rather to their insured, and steps in if that person is sued to defend them). To win, you'd have to show that the other person was at fault; caused your injury; and the extent of the injury.The problem is, a lawsuit is the only way to get more money than is being offered. Even if you act as your own attorney, you'd still need medical testimony, and medical experts (e.g. doctors) can be expensive to hire--you might spend more on the lawsuit than you'd get back.