If you have never been in this situation before, you should contact a personal injury attorney in your area to assist you. They can help you walk through these steps with you. You don't want the insurance company to take advantage of you.
I agree with my colleagues, you should definitely speak with a PI attorney. Uninsured motorist claims are pretty adversarial and your insurance company will try to settle for as lowest amount of money as possible. It's best to meet with an attorney who could review your case and put forth a strategy to maximize a fair award for you.
First, seek medical attention if you were injured. Second, you should contact an auto injury attorney for a free consultation who would be able to advise you and walk you through various steps. Many local attorneys listed on Avvo should be able to schedule you for a free consultation. Sorry to hear about the auto accident and how the other insurance company is treating you.