There are usually T & C's on those coupons. If the item you purchased complied, not all items do, then it would have appeared at eBay checkout on the left hand side, way lower down that page and easily missed. You may have needed to activate it?
There is no phone number for eBay, it's a Call Back system , lines are open now for ' live agents' , though not sure how they can help you now.
If you wish to contact CS, I strongly recommend contacting CS 8 a.m. on a weekday when the lines open for ' live agents' as then, 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=5190
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.
@dean231266