That depends - are they really a competitor in the same industry, and their use of your trademark leads to confusion in the marketplace? Because then you're not out of luck at all, you have a trademark case.
DNS is not private land; it's a system in which the existence of a TLD is dependent on the widespread agreement to grant registrar(s) the right to administer it. Movement away from reasonable and non-discriminatory behavior is an attempt to secure undue control over a system that exists only because of the participation of the internet community at large.
Of course, given the massive growth in internet consumers and the general impossibility of their all being educated (much less having a voice in these sorts of decision), this sort of abusive behavior is quickly becoming par for the course on today's internet.