Check in the transaction details (can be found in the dropdown next to the item in your purchase history) and see what the dates say in there. It may well be different to what was in the listing. As it hasn't been posted, it's possible those dates will change each day, so may not be accurate. Try contacting the seller again and ask them to send you a cancellation request. Point out that they will get their fees back by doing it that way. If they allow a dispute to be opened, they will lose their fees. It's worth a try and will speed things up if they agree.
If you can't open a dispute through the eBay money back guarantee, try and open one through PayPal. Log into PayPal, find the transaction in the resolution centre and go from there.
