......he wins.  And, that's all that this fellow is interested in:  winning. 

If you are experiencing extreme anxiety from this, it might be a very good option to consider some counseling therapy just to help you get your bearings straight, and to learn coping and management techniques.  Once your confidence increases as you gain management of this anxiety and fear, you response (or, non-resopnse) will be comfortable and he won't matter.

For now, ANY response will be giving him what he wants.  I read that you're unable to block all of his emails, and that is truly a shame.  But, you can ignore his attempts to contact you, on every level.  Don't even read them - I know it's a challenge to simply delete them, but once you do it a few times, that will become easier and easier to do. 

I am SO sorry that you're experiencing this and, please, understand that your reaction to this is very typical for those of us who have experienced trauma, particularly when it is the individual who caused the trauma that's trying to get back in. 

Brightest blessings of courage and comfort to you.