Here is a link for dealing with purchases that have gone from your purchase history.
Removed listings | eBay
How long is it since you ordered it? There will be an estimated delivery date on the listing when you boght it - if it's longer than 30 days ago this will be the reason it has gone., so you'll be out of time to use te ebay money back guarantee.
If you paid via Paypal you can claim a refund in your Paypal account.
