Go to the members section and login, if you haven't opened an account do so with the same email address you provided when making the download edition purchase.
Chances are your copy was registered to that email address as a username when you made your purchase and if you can login there, go to "My Products" then "View Registrations" and your activation key should be right there.
If that doesn't work go to the Customer Support section and leave an inquiry stating you problem the way you did above. But be sure you provide the same exact email address you provided with your purchase.
Good luck