You can't get blood from a stone. Sounds like he is trying to bully you. Try rational means and as necessary it might make sense to take it public if you have enough of a chorus of people saying this is not warranted and have exhausted all other means.
Do not heed this post. Under no circumstances should you take it public before it's seen a courtroom unless you have been advised to do so by a competent lawyer.
(It is no-true-Scotsman territory to note that no competent lawyer would ever do this. It is also accurate.)
Try to get some pro-bono help first.