Bob DBF
Contributor
I don't consider this blackmail. I consider it warning them of a pending review you plan to share, and some simple fact-checking.
As soon as you get into you do or else I'll do this to you, seems to be in a gray area that could turn into real trouble.
I'd just document the problem, and if I am not getting satisfaction, I'd warn others. No demands, no threats and no warning of what I will do. I would be, as jringold advises, be the the biggest PITA they have ever had, with respect and panache.
Bob