Do you have the original release of D2:ED and the add-on FoV, or the combined DKS release?
Did you email support@larian.com?
I assume you checked your spam folder to see if the email with the activation key was miss-identified? If you log back in to the site you bought it, is the number listed somewhere?
There is a large
Flames of Vengeance to Dragon Knight Saga patch, which I assume would allow you to use the
Dragon Knight Saga DRM free patch, so you wouldn't need the activation number any more. If you wish to continue into FoV with an existing character from the original release of D2:ED, though, you would not be able to due so after installing the conversion patch (too many changes in the remastered version of DKS). If you have DKS, though, you just need to make sure it is updated and get the DRM free executable.