If you are seeing the Activation Lock screen after updating your iOS device, you want try the following:
-Restart your iOS device and try to sign in again.
-Visit appleid.apple.com and sign in to ensure your password is correct. If you change anything here, only change your password. Try to sign in again on the iPhone.
-Plug it into iTunes on a computer and put in your Apple ID and Password when it prompts you (like it did on your iOS device).
-Check iCloud.com in Settings. If you see your iOS device listed, remove it from account (don't erase or hit lost mode). Restart your device and try to set it up again.
-These steps should fix most issues. For anyone else, you will have to contact Apple (1-800-MY-APPLE or getsupport.apple.com).
I hope that helps!