Okay, it looks like you have your Soft-eLicenser showing up in MySteinberg now.
Are you sure you activated your AI 7 when you originally installed it? Did you happen to delete your old Soft-eLicenser from your MySteinberg account? That would have wiped out your AI 7 license giving you nothing to “reactivate”.
I would be tempted to think that you never originally activated your software. However, I don’t think you would be getting the “activation code has been used already” if that was the case.
This is starting to sound more and more like a case for official support. Have you sent a support request?