You do not need to phone Customer Services for this, just to understand how eBay's 30 day MBG, Money Back Guarantee policy works.
Many Chinese sellers have their items listed as located in the UK, this is above board, because they are using depots / forwarding companies to send their items, and this facilitates a faster dispatch.
Unfortunately , when the more than often case arises, for returning a sub standard item occurs, Chinese sellers try and fob you off saying the item has to be returned to China, at the buyer's expense. Neither is true, and they are hoping members do not know the rules of MBG.
These are , that items need to be returned to the item's location stated on the listing not to the seller's country of registration. If it's being returned for the reason item not as described, the seller pays for the return not the buyer. and it goes back to the UK, Not China.
eBay's 30 day MBG, is written on the right hand side of every listing, familiarise yourself with it, here it is in the link below, it can save you a lot of money when buying on eBay.
https://pages.ebay.co.uk/ebay-money-back-guarantee/
@ashley2995