She won't return the license plates.My insurance company won't let me take the car off my policy until I show proof it isn't registerd any longer in my name. I cannot unregister it until I turn the plates into the DMV,, how should I proceed?

Take her back to divorce court, to get her to follow the rules of the court ( assuming this was ordered though the court.

And of course your insurance company will allow you to take that car off, it is called, cancell that policy, I can cancel any car policy I have on any car I even own and drive if I want to.

Just write them a letter telling them to cancel that policy.

She won't return the license plates.My insurance company won't let me take the car off my policy until i show proof it isn't registerd any longer in my name. I cannot unregister it until i turn the plates into the DMV,,, how should i proceed?

Your insurance company is full of it. They cannot force you to insure anything.

File a motion with the court requesting that your ex take the vehicle to the DMV and register it in solely her name.