If your vehicle was damaged while in parking gear and the insurance company refuses to pay for transmission damage what recourse does one have?

Are you asking about transmission problems that someone hit you while in park? Or that you didnt have money to fix it and asked the insurance company to help? If its the first scenario, you will need proof that the damage done to your transmission was a direct result from that accident. If its the second one, your insurance doesnt have to pay anything, as that's what warranties are for, not insurance policies.