I don't know if anyone actually told you what your issue was. I looked down and saw discussion about the import, but couldn't find anyone mentioning the actual issue. At some point after the import start time, you either first started playing Destiny on the Xbox One (maybe at a friend's house) [if your first characters are on Xbox One, then there's no import prompt as it's the very first characters you make, but after that point, if you play on Xbox 360, then the characters are starting out different and separate]. If you didn't first play Destiny on the Xbox One, then there's only one of three other things that cold have happened: The first is that you logged into your account on the Xbox One and performed the import and just forgot about it. The second and third is that someone else logged into your account on the Xbox One and either created the first characters there before you played Destiny OR someone else logged into your account on the Xbox One and dealt with the import. If the first characters you know of were on Xbox 360 and you didn't log into the Xbox One's version of Destiny after the beginning of the import timeframe, then someone else logged in as you and did such, which is why the character was already there on the Xbox One. Sadly, after the characters are separated, there is no further chance to import, so you're out of luck (as you already know from the other posts). But at least now you might have an idea what happened. If you feel it was someone else, then you might want to change your login credentials (email and password) and maybe add authentication of some sort so others can't log into your account without your knowledge.

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