Can you access your L smalls L account on your console? If you can you can access the account management section to view the windows live ID you would use to sign in. If its different to the one you used on Xbox.com then there's your problem! :)
If you cant access it on the console you would be best off contacting support at
support.xbox.com/contact-us to make sure your are using the correct sign in info. You will have to pass some security questions but they will be able to assist you better!
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