A whois search on your domain reveals that it's registered until the renewal date, which is in 2012. I don't think you're losing your domain. I'm guessing that you used to use their hosting as well until you came here. If that's the case, you're only losing their hosting, but not losing your domain registration. There's nothing else to do since you've added the domain to your account and changed the nameservers to point to x10hosting. You're all set.