If you paid with a credit card you can get your credit card issuer to take up the case for you
after a reasonable amount of time. The Visa and Mastercard Regulations require card issuers to give a merchant a "reasonable period" to resolve the matter before they can do a charge back. While "reasonable" is not defined by the regulations, it is generally accepted that this period is 28 days. If you have not heard from them after this amount of time has elapsed, call your card issuer and ask to speak to their billing disputes department. It's not guaranteed, but they have a better chance of resolving the matter with an unruly merchant than you do.
(Vlad the Inhaler forgot his password, Wed 26 May 2010, 20:26, Reply)