All sign-up, sign-in and your account/profile related matters.
Sign-up: It says "Account exists" but I don't remember signing up with the same email/FB account.
If you are signing up using email and see the "Account exists" dialog, click on "Forget Password" to reset your password and login with your new password
If you are signing up using Facebook, continue to login with your Facebook account. Check the app content and go to My Profile tab to see if the details are yours. If you are certain that your email or Facebook account has never been used to sign up for FitFit and are suspecting someone one is stealing your identity, contact us at firstname.lastname@example.org for assistance.