You need to open a case now,  this way:

If you are still within 30 days of the item's last estimated date for delivery,  proceed this way:

Go right of the item in your Purchase History and from More Actions select Return this item. Select the reason.... Damaged in Transit.

The seller needs to either refund you in 3 days, or issue a pre paid return label for the return of their item. Once the item is received, they have 48 hours to refund you.

As it is glass, and you did buy from a well known established charity, they should refund you within those 3 days without sending back broken glass.  Doubt very much they'd insist on this, if they did you'd need to contact Customer Services.

If this doesn't happen, you need to escalate to eBay, eBay step in and force the refund.

Listen to no excuses or promises from the seller to close the case early, and do not forget to escalate.

If you need to,  contacting eBay Customer Services is not easy nowadays to get a live agent , but some have had success using the app, otherwise keep typing in ' I wish to speak to an agent' and this too can work.

Use this link to contact CS, if you can try at 8 a.m. on a weekday morning also more chance there for Dublin to answer.

https://www.ebay.co.uk/help/eua?id=5190

Lines open between 8 a.m. to10 p.m. on weekdays.

9 a.m. to 6 p.m. on weekends.

@sunshine2023-2