Ask your attorney, But I don't think you have a case.
Anyone can buy any domain name as long as someone hasn't already bought it. It doesn't matter if it's a registered business or a trademark. Doamin names are wide open.
Back when the ".com" frenzy started people were quickly buying up all the names of major companies hopping to make big bucks in selling the name back to them and they did.
What they would do is, they'd buy all possible forms of the company name. Like Pepsi.com, PepsiCola.com, PepsiCo.com, etc. so they would have no choice but to make a deal.
This guy probably found you didn't have one registered and bought it on speculation. Even though he has no intention of ever using it, I think he still has to pay an annual fee to keep it.
Good luck in your fight.
Keep us informed.