My phone is hacked and I need to fix it

If you have you data backed up, try completely resetting the phone. Then restore your encrypted data.

Selling/Giving Away Device.      

You might want to consider changing your password and making sure it is a strong one. You can also add 2 Factor Authentication to your account for more security. If the attempts continue, you might want to consider a name change.

Link to contact Apple Support in the article.

Apple ID has been compromised.      

Security and your Apple ID.     

Checklist: If you want to see if anyone else has access to your device or accounts 

 Apple ID Password Change.     

Note the restrictions in the article.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.

Apple ID -Two-factor authentication          

Two Factor Authentification availability.    

2 Factor Authentication - How to generate a recovery key

Apple ID - Using app-specific passwords.     

Apple ID - Two Step Verifications FAQ