I usually would go straight to the throat and very personal.
Publish their letter on the domain they seek, capture all lawyer and company details and publish to site.
Use opsec for phone numbers, call them at terrible hours ( at home) to discuss offers of payment.
They are trying to bleed you with superior resources so guerrilla tactics are best ( legal of course)
They act different when they realize they are exposed and you don't care about normal processes.
Lol, I should make my own David v Goliath service.
Depends on the size of Goliath. No one scary came for me and a few 2am calls led to crickets.