eBay ' divorced' Nectar last month , so any purchase of an eBay item needs to be done through Nectar.com have you tried to buy an eBay item that way, and see if those points exist there?
I would imagine this is a Nectar issue to find lost points as they are the ones who issued them, but eBay and Nectar are renown for blaming each other over issues, and I very much doubt contacting eBay Customer Services will do any good as said, eBay are no part of Nectar directly anymore.
Perhaps as with eBay Customer Services, you can get a good helpful Nectar agent, and one not so, maybe try Nectar CS again, and hopefully get the answer you are seeking.
@elfury