Disable Apple ID
When I'm trying to update my iPhone I'm getting a message display that my Apple ID is disabled
iPhone 6s Plus, iOS 9.3.4
If it’s been disabled for security reasons then resetting the password might fix it : If your Apple ID has been locked - Apple Support
You might then need to log out and back into the account wherever you're using it : What to do after you change your Apple ID email address or password - Apple Support
If that doesn't fix it then contact iTunes Support : https://www.apple.com/emea/support/itunes/contact.html