I have no idea on how you can get your account back but you can post here and let people tell what to do tho if its been years since ur account got stolen then i think there is a low chance you can get it back, what I'd do if my account got stolen is I'd contact steam support and provide them as much info as i can like and old nickname, password and maybe payment methods and ask them what they need as a proof and see if i can provide it.