How to loosen eccentric BB shell?
Yours looks like the one described in this blog post: https://handsonbike.blogspot.com/2013/11/avanti-inc-3-eccentric-bb-for-belt.html?m=1. 
The writer was able to free it up by putting the bolt partway in and hammering it, so I would try that.  It’s the same principle as old quill style handlebar stems.