Contact half.com and ask for an update of your situation, or dispute the charge with your credit card company.
But "You may not contact the seller or submit a Buyer Protection Policy Claim to Half.com if you have instructed your credit card company to charge back the disputed item. Buyers who go though their credit card company to dispute a charge may loose their privilege to buy or sell on Half.com."
http://pages.half.ebay.com/help/policy/guarantee_p.html