You or any other person who may have access to your device may have inadvertently tapped "Get Started". See the image below
By going to Settings > General, Scrolled down and tap Transfer or Reset [Device], Under "Prepare for New [Device]", tapped Get Started.
Source: Get temporary iCloud storage when you buy a new iPhone or iPad - Apple Support (IN)
If you feel an unauthorized person/app is remotely using, controlling or monitoring your device, then that is possible only if you have done one or more of the following Don'ts...
- Don't hand over an iPhone to kids or to a stranger without Enabling Guided Access
- Don't share Apple IDs
- Don't Jailbreak
- Don't share sensitive information pertaining to your device
- Don't give in to Phishing
- Don't plug in your device in Airports and Public places through third-party cables and trust the device. Beware of Juice Jacking. (Especially in India)
- Don't leave your iPhone unlocked and unattended in public places like offices, schools, malls, etc.
If one of the above is true then quickly change the Apple ID Password and Return iPhone settings to their defaults.