How can I get my ex to authorize a payment for insurance if his name is still on the title?

My ex bought me the car then we split up after 5 months. He told me I could keep the car as long as I took over payments. I paid on it for two years then completely paid it off earlier this year. He agreed to get the title transferred but he hasn't done so yet. Two weeks ago I totaled it and now my insurance company is telling me that they can't give me the money without the title holder's authorization. When I finally got ahold of him he said he's not going to release it and that since it's in his name still he should get the money. What can I do? I only have two weeks left of my insurance company paying for my rental car and have to get something lined up soon.