Is this the screen you see when trying to activate.
Have you tried any of the suggestions contained in the link I posted earlier, for example restarting your device, attempting to connect to wifi or attempting a Restore?
Who suggested DFU mode, was the intention to Restore the device via iTunes, if so what happened?
I've only found one possible fix which involves Restoring device without the sim installed as per below from this discussion.
Unable To Activate iPhone 7
But I'm doubtful that will work because others have reported that may cause a boot loop.
The only concrete solution was a Reddit post which involved taking the device in to Apple who swapped it over, they say the issue has something to do with the logic board!
https://www.reddit.com/r/applehelp/comments/9ja2k5/an_update_is_required_to_acti vate_your_iphone/
I would suggest if you have attempted to Restore the device via iTunes but can't for whatever reason or when you did it made no difference, then your only option is to book a Genius Appointment. Don't try and discuss the issue over the phone, this needs to be dealt with in person, also have some evidence regarding others experiencing same (ie links to Reddit and Apple forum discussions).