Activation key expired

Around a year ago we bought 25 licences via a software supplier (scienceplus). We distributed the licences trough email to all the employees that wanted to have Fences. One employee only recently used her license key but got the following message: email adress is not valid for the product key. The productkeyretrieval webpage won't work for us because we have a list of productkeys but no linked emailadresses.

How do we proceed?