This happens when someone signed in/up with a different email than they used to create the plans. Check the email you used to sign in or up with (Click "Account" under the homepage). If it's the wrong email or you think you might have used a different email to create your plans, click the power button in the upper right hand corner to sign out. Sign in with the other email.
Not sure what email you possibly used before? Most often, it's your person email if you signed in with your school/work or vice versa.
Think you know the right email but forgot the password? No problem -- click "Sign In or Up" on the homescreen and then click "I forgot my password or need to change it". You'll receive an email with a link to reset your password.
Still struggling to access your plans? Click "Contact Us" in the upper right hand corner.