Take them to small claims court for an amount below the appeal threshold. If they ignore you get a default judgement and ask a sheriff to go to their offices and seize enough assets to guarantee an auction will cover your award plus costs - return the excess to FB.
This has been done a few times and draws their attention.
The downside is for FB, these courts were set up to defeat ignore-trolling by FB, among other things, after all their careful neglect of user problems IS a Trollform...
https://wildwest.substack.com/p/the-guy-who-beat-facebook-in...