Is this to collect from a Click & Collect collection point?  Then, if it's not in your emails,  eBay messages or order details,  the do contact eBay Customer Service for this important number as the store will not release the item without it.  
 
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 recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
 
 
@linbri72