Email of Username

I have decided to try and find my old LoL account from when I tried League out back in 2012 ish.... now my old email address is apparently registered and everything but whenever I check it for my Username (when I go forgotten username) no email has been received. I unfortunately do not remember what my username was because it was from so long ago and from when I was a young age. Is there any reason why I'm not receiving the email containing my username?
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