Has the email now arrived?
I had the same problem with a Yahoo user three days ago. She registered with an alternative Gmail address and then yesterday I saw her registration come through on her Yahoo address.
This wasn't a case of missing the spam folder. I went round to her house and double checked and together we attempted a re-register on her Yahoo address and the confirmation email did not arrive.
Such unreliability is one reason why I have largely abandoned my Yahoo addresses. Too frequently, mail gets bottlenecked and turns up up to 72 hours late to some YahooGroups.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.