A seller is not able to close shop /close their account if they have made recent transactions , if they are no longer registered as a seller, this means eBay have removed them from their site.
Contact eBay, looks like they made a courtesy refund if you received this before sending the item back, but contact them to see what you need to do with the item.
This is the easiest and quickest way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open 8 a.m. - 10 p.m. on weekdays
9 a.m. - 6 p.m. on weekends.
Automated agents will be available on chat outside of the above hours.
I recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@jammun_55