..iLoveLife11..
Perhaps if your device was purchased 'as new' + IF someone
else set it up first.. Then did not return the product to first user
status, before you personalized the software? Then, may be
vulnerable to some outside influence and never be safe.
A fully new installation in the device should remove any other
user access and free up that device as new; unless you have
a compromised backup, which may reintroduce same issue
and not get rid of that source of an issue.
Restore your iPhone, iPad, or iPod to factory settings using a computer - Apple Support
//support.apple.com/en-us/118107
Had you attempted to re-install the system w/o backup (&/or
clear the device and start afresh) then change all passwords
and make new user there? Symptoms may appear to you, as
though the iPhone were hacked; but you'd be incorrect.
[Just some thoughts. If you got a secondhand device that
wasn't prepared for a new user account, it would be locked
Without original buyer/owner credential, to authenticate.]
Maybe get appointment with an official Apple store staff
or authorized Apple service repair center, to seek help.
You would need to have and take along official proof of
purchase from a reseller or Apple, for them to help you.
Different process may be utilized outside of steps here.
