Yep, you keep the item. If you have received a refund and the case is closed, the seller seemingly did not wish for the item to be returned, before refunding.
Personally, I would keep the item safe for a while in case the seller being new, and not undertanding the rules, wishes for the item to be sent back.
Nothing to enforce you to do this, but if you wish to, the seller needs to first send you enough postage cost to cover a tracked return postage. but again, you are not obliged to do this, as the case has closed.