All you can do is contact support. Not sure how much help they will be considering the fact that both the original account owner and the player that took the account are in violation of the game rules.
"3. Account sharing
Players must keep their own login data, passwords and access data secret. Disclosing your password to other players is strictly prohibited.
As a player, you can only play your own account. Accessing another player’s account is strictly prohibited.
Make sure to choose a secure password and remember it is your responsibility to keep it secret. Please inform us promptly if third parties gain unauthorized access to your account.
If someone gives you their own password, please report them."