I think my iPhone is hacked

Why do you think your iPhone was hacked?

No, if you haven't jailbroken your iPhone, it's not possible.

To keep your Apple ID account secure, see the following Apple articles: 

If you think your Apple ID has been compromised

If you think your Apple ID has been compromised - Apple Support

See who has access to your device or accounts

See who has access to your iPhone or iPad – Apple Support (UK)

Delete suspicious content from your devices

Delete suspicious content from your devices – Apple Support (UK)

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

• if you see devices that don't belong to you, delete from your account.

Personal Safety User Guide -> Personal Safety User Guide – Apple Support (UK)

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

(if you haven't already done this) Two-factor authentication for Apple ID -> Two-factor authentication for Apple ID - Apple Support

Change your Apple ID password -> Change your Apple ID password - Apple Support

• Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger. 
• Never provide your password, passcode, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

(Since this was re-titled and no one had replied, and I don't use premade

contents; here I have made a new reply to this thread; well before now.)

Curious if your recent iPhone had been set up ahead by an original owner

and maybe that earlier account had not been removed before re-selling it.

If you try to re-activate it as new, if not prepared correctly; the iPhone may

show later as Activation Locked and not able to go ahead; without original

owner's pass-code. Needed then to be used to unlock the Locked Device.

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

//support.apple.com/en-us/HT201351

"Use these steps to transfer information to your new device and, if

applicable, remove your personal information from your old device."

[Steps a re-seller should've done before you bought their used iPhone.]

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

//support.apple.com/en-us/HT201365

..And because this thread was re-titled, I'm not sure what's going on there..