Why did you include emails threatening to blackmail Simple AI to get more money ("wondering what a fair exit package looks like ... and what I should post on Linkedin to update my network"), then indicating that after you received $20K in payment, you "wouldn't bother" them? All of this following a him-or-me demand email.
And then making this post? It's a pattern of self-destructive behavior.
The best possible course of action at this point is deleting the blog post. Note that the separation agreement you signed prohibits you from sharing any Separation Information—including consideration (in this case the $20K figure you reference is part of the consideration). Your blog post is public evidence and even this comment I'm making right now could end up in discovery if your former employer wanted. If I were you, I would not antagonize them further.