If I found myself in your position, I would call the insurance company, as it seems you did, and try to find out why exactly they are not paying. What specifically does their policy say, and how do they perceive that you do not qualify for their paying that expense? It sounds like the answer is that they found the ambulance ride to be "not medically necessary."

Next step, I suspect, would be to appeal their decision and submit documentation that it was, in fact, "medically necessary" and you could not "drive yourself" as they concluded.

If you have not done so already, call the insurance company and make sure you understand all of their deadlines and the proper procedure for this kind of an appeal. Insurance companies are out to make money and will screw you over if they can. Don't let them!

Sorry to hear about such a financially scary and frustrating situation.