Did you return the item with Delivery Confirmation, or did you just send it cheap-o mail and 'trust' that your seller would do the right thing? If you did not use Delivery Confirmation there may not be much you can do.
When there is a problem with an item, the usual process is to contact the seller, and if still no satisfaction (promises of compensation are not worth much, are they) then open a claim in the Resolution Center. You will usually be required to return the item at your own expense, - Delivery Confirmed. The following link tells you all about it, see Section 4:
http://pages.ebay.ca/help/buy/item-not-received.html
If, when you mailed it, you got some sort of shipping number - whatever is on your postal receipt, you can try to enter that into the dispute. If it's not a real Delivery Confirmation number, though, don't get your hopes up. Or if you used a credit card you can call the 1-800 number on the back of the card and ask to do a chargeback. You'll need to have all these transaction details in front of you when you call. The credit card chargeback is usually the last resort if the Resolution Center cannot help you.
You have only 45 days in which to open a claim, and I suspect the seller knows at this point that there is nothing further you can do. Without that DC number, you cannot prove the seller has the item back.
What about feedback? You have 60 days in which to leave a civil, rationally worded summation of your experience with this seller. Do not let that day expire, - not if you can avoid it.
