Look to the case, tracking should have been added if the return label was used, if not see if you can add it, then escalate 48 hours after it shows delivery, if not refunded beforehand.
If the above is not possible, then contact eBay Customer services explain your findings. I do recommend contacting CS only first thing in the morning when the lines first open at 8 a.m. for ' live agents', as there's more chance of Dublin answering.
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.
As said I, recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@trumpeteom