The Xbox account is apparently linked to an Epic account, but I have no idea what account that is. What are my options?

I am trying to play Fortnite on PC with an Xbox account (so I can keep my stuff from when I used to play on Xbox a while back), but on trying to link my Epic Games account (which I have had for ages) to Xbox, it says that the Xbox account is already connected. The Microsoft account website agrees.

When I then signed in to Epic Games via Xbox, it asked for the email for the linked Epic account, which I do not know despite trying all of the emails I have ever used. I do not ever remember linking an Xbox account to Epic and have never used an Epic Games account other than this one. What are my options? From what I see, unlinking the Epic Games account will remove all my game progress, so I may as well not bother if that's the only option. Should I contact Epic support? Has anyone had experience with this before?