Hi, welcome. Unfortunately the serialnumber of the controller will not help to provide a license as the bundle was created by the manufacturer. So MixVibes doesn't know your license key as you apparently didn't register it in the past.
If you have a prove of purchase you could try emailing this to
support@mixvibes.com.
An alternative would be to purchase the current 'Cross DJ' at the discount price €49,-. As Cross LE latest version is 2.6.
This is fully compatible with current OS and has the benefit that it works without having the controller connected.