Hey LuS.h, welcome to the forums! Sorry to hear you're having trouble getting the correct Xbox account linked to your Ubisoft account.
This is something we're not able to help with here on the forums, where messages are public. We need to look at your account, you see, which concerns your personal data, so that has to be done in a private chat. Fortunately, you can get in touch with us via social media, or on our support site, at the links below:
Facebook PM
Twitter DM
support website
When contacting us, be sure to include your Ubisoft account username and email address, so we can quickly find your accountThanks!