At first try to reset your password according to this instruction: How to reset my password.
In case you succeed and set a new password, the problem is solved. Log in to your account, go to security settings and terminate all active sessions if there are some.
Additionally, you are encouraged to protect your account with 2-factor authentication (2FA) and to follow our recommendations on maintaining highest security in order to avoid future hack attempts:
Should you experience any problems with resetting your password, please contact us by leaving request here: my account was hacked.
P.S.: In case you just want to delete your account, feel free to submit the request here: I want to delete my account.