Dilemma over eBay return

So we bought a Valve Steam Deck on eBay which was advertised as the 512Gb model. What arrived was a 64Gb model so we started a return immediately. The seller had changed their status to on holiday until mid May. We followed eBay rules regarding return and returned the package (signed for tracked 1st class). They attempted delivery three times but nobody would sign for it and it was sent to Belfast sorting centre. Meanwhile eBay gave us a full refund. Today the steamdeck has been returned to us and my question is what now? Do we have to return the item back to seller? Are we at fault for keeping it? As far as eBay is concerned it's done and dusted.

[edit]Seller had the opportunity to accept return(to a different address other than the return address)but still thought they could scam us by not signing for it. This meant the tracking showed fair attempt at returning it and eBay took our side and refunded. Play stupid eBay games and win stupid prizes. We will keep hold till May and if we hear nothing from the seller(not expecting to) then we will sell it.