You would have to dispute the registration with ICANN
http://icann.org/en/udrp/udrp-policy-24oct99.htm
I believe that ICANN arbitrations cost between $5000-$7500, depending on
complexity, which includes substantial filing fees paid to WIPO
http://www.wipo.int/
Basically, this would only be worth pursuing if you have a trademark, if you don't then the likelihood of winning the case is slim.