Did you by any chance return it with Delivery Confirmation? How long ago did you buy it?
When a seller refunds, it goes back the same way it came. Meaning if you used a credit card it goes back onto your card. It may take a couple days to appear, but you will get a notice in your regular email that the payment has been refunded. It is automatically generated, - the seller does not send it. So if you do not have that, you have not been refunded.
Same as if you paid with a paypal balance, - the money gets put back. The seller does not choose how. How long ago did you send it? Will the seller have had time to receive it?
If you did not use Delivery Confirmation, the seller could say "Return? What return?", so you will hope your seller is honest. If you wish to see what the official procedure is for returning items, the following link will explain about filing a Not as Described claim, - see Section 4:
http://pages.ebay.ca/help/buy/item-not-received.html