I would add to those excellent tips: Stick with email and avoid talking to your ex. Communicating with him via email offers several advantages:
Instead of firing off an angry verbal retort, you can get your thoughts down in an email and vent as much as you want without further angering and alienating him.
Then reread and rewrite the note so you sound cool, calm, and mature.
Let it sit, re-read it again from his point of view. Look for signs of anger, provocation or edge. Rewrite it and eliminate those. Pissing him off won't get you what you want -- which is his cooperation.
Once you send it, you have a written record of your communications, and you never know when you might need that.