If you paid for the coins with PayPal, file a buyers claim against Kixeye, especially if you had any coins in your account when they closed it.
If you paid for the coins with your credit card, file a claim against Kixeye with your credit card provider, especially if you had unused coins in your account.
Also, file a complaint with the better business bureau http://www.bbb.org/
The BBB will act as an agent in the disagreement on your behalf for free.
If you're not satisfied with the results, that goes against the company and becomes part of their
permanent record both online and offline.
After enough BBB complaints, their rating falls.