lost account

hello, ive been playing this game for many years now and ive wanted to expand my gaming knowledge with my little brother hes been very interested in this game and you guys have recently sent a message to everyone that logs in to change their username and my brother changed it without any logic behind it so hes forgotten his username and i would love if u would respond to me as quickly as possible so i can recover this account especially since ive spent a lot of money on this game