When I have had to get a refund from a dodgy deal (obviously fake seller without the product, using photos from a different auction), Ebay wouldn't do a thing until after the expected delivery date, presumably to ensure that it really was a bad transaction.
Perhaps that's the problem here? Ebay won't cancel the sale on your say-so this soon, and maybe the vendor is running up against a similar issue on his side.
Having said that, I won a cheap laptop for 50p and unsurprisingly the vendor turned out to have sold it elsewhere the day before and 'forgotten' it was listed on Ebay. He refunded me and the sale remained unpaid until... well, it probably still is. Doesn't appear to have done me any harm, and at least I was the allowed to give him a serious neg (his only one, but every one counts nowadays).