First of all, we're sorry to hear that this has happened.
To stop unauthorized usage, you'll need to change your password as soon as possible. Once you change your password, all current sessions will be logged out. This means any users will need your new password to access OpenAI services.
How to change your password
Log out of your account or use an incognito browser window.
Head to the login page and select 'Log in'.
Enter your email address and continue.
Click 'Forgot password?'
You'll receive an email containing instructions to reset your password.
If you have logged in with Microsoft or Google authentication, you'll need to reset your Microsoft or Google account password.