You need to follow the basic guidelines and tips to keep your details secure. For instance:
Don’t leave your Apple device unattended.
Secure your device using a fingerprint scanner or passcode.
Change your passcode often and immediately if you suspect any unauthorized activity.
Ignore unsolicited messages asking for your personal details or passcode.
Register and learn to use “Find My iPhone” to locate, lock, and delete your private details from your stolen phone.