First, contact the seller. Gently explain what has happened. Quite often the seller will help you and the two of you can arrive at a suitable outcome. If, however, the seller is no help at all, or promises to do something but doesn't, then you may need to open a 'Not as Described' dispute and escalate to a claim when able. The following link tells you more about it, see Section 4:
http://pages.ebay.ca/help/buy/item-not-received.html
Just remember you must take action no later than day 45 from when you paid, - best to do it no later than day 43. You may be asked to return the item at your own expense with Delivery Confirmation. You enter the number into the claim and when it shows the seller got the item back, you get your refund. That refund includes original item price + shipping fee, but not the return shipping fee.
You have 60 days in which to leave feedback. The more civil you are in simply stating the facts, the more likely you are to be believed by other buyers.
Good luck. 🙂
