eBay do not answer ' messages' it's a Call Back option.
If the return window, the case has closed , you cannot open another for that item with eBay, you'll need to turn to your payment provider for help with your refund now.
For future reference, 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 do recommend contacting CS very first thing in the morning, when the lines first open, as there's more chance of Dublin answering.
@pjelec33