Usually this is done because of bad, possibly even fraudulent behaviour on the part of the seller.
File an Item Not Recieved claim through the Customer Support up in the top right hand of this page. Tell them that the item has been removed. You will need the listing number. You can find that in your Paypal account.
Usually this gets you a prompt refund.
If the seller was not acting improperly (and eBay occasionally ends a seller's listings if he has not kept his credit card information up to date) when the item arrives you can refund the refund through Paypal > Send Money.
