how did you purchased the product? (i.e.: bank debit card, visa, PayPal)
If you paid by PayPal, you need too use your email that you used for PayPal login account.
if you used a different email than you used to login to Forum's, you can contact Stardock Support and they can get your email addresses merged.
Support Link: https://www.stardock.com/support/?from=nav