One thing to be aware of, even if you suspect that the seller may well have relisted the items you've paid for, is that it's also possible that he/she has more than one identical item available for sale. If this is indeed the case then that would account for the identical listings, as the seller may well have just chosen to relist the advert again to represent the additional identical items that are still available for sale. If, however, this is not the case then either there's been a glitch that has resulted in the seller's sold listings relisting as if they had never actually sold, or alternatively - and more likely - it may well be that the seller felt that the goods didn't fetch enough money and therefore he/she has decided to relist the items.
If the last of these options does actually happen to be the correct explanation as to why your purchased items have been relisted for sale then the seller has breached the terms of the contract that he/she entered into once you paid for the items. As soon as you paid for the items you became the legal owner of the goods in question, and therefore the seller has no legal right to offer them for sale to anybody else.
Finally, you say that you've taken screenshots of the listings in question just in case the seller comes back with something like "Oh, sorry, your items got lost" but have you actually checked the listing number in the live listings when compared to the item numbers of the items you purchased? If so then send another e-mail via the case cross-referencing the item numbers against each item - ie: the item number of each item you bought, with the item number of the current listing for the same item. Do this one by one for each item. As laborious as it may seem, if it does turn out that the buyer has tried to resell the exact same items that you paid for, then by referring to the listing numbers in this way it will make it extremely difficult for the buyer to talk his/her way out of the matter and come up for an plausible explanation as to why your items have been relisted for sale, especially as it would be so obvious to anybody reading the case details that you've cotttoned on to what the seller's doing and have caught him/her out.
If that is indeed the case then I suspect that the seller will go silent and refuse to respond to any of your messages so as not to implicate himself/herself any further. If so then just let the case get to the point where you can escalate the matter to eBay, then as soon as you get the chance to do so escalate the case to eBay so that they can have the final say on the matter. I suspect that you would end up getting your money back in full, as eBay wouldn't want to be seen to be helping a dodgy seller to cover up an attempt to deny you the items you'd paid for and resell them on to somebody else if that is indeed what he/she is trying to do.
