Hey Demon, welcome to the forums! Sorry to hear you're having trouble launching Siege.
Usually, this happens if the game is activated on another Ubisoft Connect account than the one you're signed into. Please get in touch with us via one of our direct support platforms, linked below, and one of my teammates will be able to have a closer look at your account and help you get it sorted. Please be sure to include your Ubisoft Connect username or email address (and include those of any other accounts you recall having) if getting in touch at these links, that really helps speed up our support
Facebook PM
Twitter DM
support website
Let me know if I can clarify that at all - I'm confident you'll be able to get it sorted soon at the links above!