iPhone 7 plus hacked?

The most likely explanation is your device passcode is known, or somebody got your finger on Touch ID without you realizing it.

Change your social media passwords and particularly change your device and Mac passcodes.

If your devices are showing weak- or known-password-related errors and maybe you’ve re-used some passwords, start fixing that now; use new and unique passwords.

iOS / iPadOS devices cannot be hacked or infected with Virus / Malware / Spyware if it is updated to the latest iOS/iPadOS unless you have intentionally downloaded spurious software or unauthorized apps directly from the internet and installed on your device or/and have Jail Broken. 

It (Hacking) also depends on how careful are you in sharing sensitive and valuable information pertaining to your iPhone such as Passcode, Password etc with your friends and family members.

Be careful when sharing the device's sensitive and valuable information with friends and family members.

Thumb Rules:

1. Enable  Guided Access before handing over an iPhone to kids
2. Don't share Apple IDs
3. Don't Jail Break
4. Don't share sensitive information pertaining to your device and payment methods
5. Beware of Phishing

Your phone has not been hacked, but your Whatsapp or Facebook Messenger account could have been. Change your password on your social media accounts.

Scams or scam attempts.

Ignore or delete them.