If you search for the item by using the listing number and nothing shows up, it means that eBay has removed the listing. You only have 45 days from the time you paid to open an item not received dispute, don't let that time limit expire.
you can Al's check the seller's feedback page, if it says nit a registered user, it means that eBay has suspended or closed the seller's account. If this is the case, open an item not received dispute as soon as possible. State that the item has been removed by eBay and the seller is not a registered user, it will speed up the refund.