I didn't have a Stardock account at the time of purchase, but I made one right after because I noticed the option to activate Fences with my account.
End of Hope12's quote
Your Stardock account IS associated with the email you used when you purchased. Purchasing created the account for you. You must use the info with which you made the purchase.
https://esupport.stardock.com/index.php?/Tickets/Submit
Go to that link, create a support icket.
Wait for a human response via email. Don't reply to the automated email, doing so will move you back in line.