I would write a formal letter to the board of directors (and perhaps key external shareholders) as well. It doesn't have to be much - even a forward of the post

I would write a formal letter to the board of directors (and perhaps key external shareholders) as well. It doesn't have to be much - even a forward of the post, letting them know that it refers to you and their company. If they are complicit - it makes a paper trail for others to discover. If they are not complicit then the CEO will get instructed to do the right thing.