You are a Private seller, did you not use a Simple Delivery label?
Under SD rules if the buyer opens a case for item damaged in transit , eBay pick up the refund, they pay the buyer , and you get to keep the payout.
Yes, it does sound dodgy what was actually returned, but no matter, if it was claimed damaged in transit and SD used, you do not pay the refund. Or, did the buyer open a case for item not as described?
If Simple Delivery was used contact eBay Customer Services ask why you paid the refund, when they should have covered this cost.
I strongly recommend contacting CS 8 a.m. on a weekday when the lines open for ' live agents' as then, 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.
It's not easy to get through to CS, you just have to have perseverance! Instead of a quick option, 'Contact Us' which put you direct to a CS agent, you have to scroll past ' How Can We Help you today, to the very bottom and click on the Contact Us below Need More Help?
That takes you to an annoying AI bot but if you persevere keep asking questions it cannot answer and Insist on an agent, they do finally put you through and say .... waiting time ** minutes!
@saroy_8756