Didn't the Post Ofice explain why the item was not accepted, what was wrong with the label? It might have been issued with an insufficient weight ?
Try another Post Office. If they too refuse the item, ask why, and you may then need to contact eBay Customer Services to reissue the correct label, and they'll charge this to the seller's account.
This is the easiest and quickest way to contact eBay Customer Services from the link below, for a Call Back option. I do recommend contacting CS very first thing in the morning when the lines first open, as there's more chance of Dublin answering
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open between 8 a.m. to10 p.m. on weekdays.
9 a.m. to 6 p.m. on weekends
@lisiliff4
