I never understand how a seller is allowed , is able to , offer such a large partial refund when an item is being returned for the reason not as described , reason that it was badly damaged on arrival.
All I can suggest, is to contact eBay Customer Services say the partial refund is unacceptable, that under their 30 day MBG you are entitled to a full refund when receiving such a badly damaged, and therefore useless item.
I strongly suggest contacting CS only very first thing in the morning when the lines first open at 8 a.m. as 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.
Good luck and please do come back and tell us how you got on, only speak to Dublin, any other agent may well agree to send a full refund to you, and it's an empty promise !
@chronocollectibles