Ask thim to go and f**** someone else. Try to send them an offer.
To my knowledge,
You are not using that domain to tamper their growth or spoil the reputation or try to run similar service or advertise any other casino who are their copetitors.
You registered that domain in good faith without any intention to curb the business of Casino de Monte-Carlo casinos.
And they have the trademark only for Casino de Monte-Carlo and not for montecarlo-casinos.com.
Send them a 1000 dollar negotiable offer.
Regds.,
sarathy.s