My condolences you've probably been had. The rate of fraud on Ebay is much higher than they tell everyone. Go here to request contact info, they will send you a name and phone number.
http://www.ebay.com/help/confidence/...r-contact.html
[1] Call the seller and ask for an explanation
[2] file a complaint with Ebay
[3] consider filing a complaint with USPS for mail fraud
document and keep records of everything and all contact with the seller