Hello. I am sorry that you had this experience with another player.
As you stated, there are many users who share this name. By chance, do you happen to have a replay of your game with them?
In either case, during a game or in a replay you can right click the user’s name, image, or life point bar and you will get a notification of “User ID copied to Clipboard”. This will allow you to paste their specific discord user ID that can be tracked even if they change their names.
Again, we hope that you don’t run into this experience again, but hope that this tip helps you in any future reports should they be necessary.