What to do when the popup still appears after disabled the "Find my iPhone"?
1. Please tap the Home button of your iPhone twice and end the Settings process. Now restart the phone.
2. Go to Settings>iCloud and make sure that Find my iPhone is disabled there.
3. Open Safari and navigate to a random webpage, to ensure that your iPhone is connected to the Internet. Another way to test this would be to go to Settings>Wifi and switch to another network connection.