I have a time machine will u use
Did you talked to them on a game chat, or through private messages?
Then it should be on your inbox . Check again .
You can see the history of all private messages. If you're on desktop, go to the right upper corner, and you'll find your username. Click on it, and a window will open. The first option says "profile", and the second one "messages" (or something similar, as I'm translating). Click on it, and you'll see all of your private messages, then just search for the conversation and you'll see their username there.
Well I sent a team message I couldn’t see it.