You need to add the tracking to that return case so it's shown as delivered back to the seller. The seller would then have 48 hours to refund you.
If you cannot add the tracking contact eBay Customer Services they should be able to do this for you. Also, they were your first port of call too, to request that correct return label.
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.
@anthonmcdonal_30