itsme® only works with the unique combination of your mobile phone, your SIM card and your itsme® code. As a consequence, the new owner of your mobile phone will not be able to use your itsme® account, since he doesn't have your code nor SIM card. You can easily reactivate your itsme® account on your new device. First, block your account via this website . Once done, reinstall the app and register again.