I looked through the Spybot website,and couldn't find anything written about what to do in that situation,so this is a bit of guessing on my part.

If you used webmail(gmail,outlook.com,etc),you could probably find the email you originally received about the download details for Spybot + AV,if you kept the email,and see if the link in it still works.
If the email you used is on your computer,and the email from Spybot was deleted when you reinstalled your operating system,then you would probably need to contact them.This is a link to their contact page:
http://www.safer-networking.org/contact/