This is happening to me similarly but I don’t know the email to the epic games account. My only clue is the username and when try to enter a email it lock me out and give me an error code
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Contact Epic directly and see if they can help. If you're in the same situation (linked account you cant access) see my other comment - there is a way out but it comes at the cost of redeem code emblems and some other things like bungie account-bound rewards