Here is an actual Chat I had when a new iPhone X we bought was not activated at the store... (I finally gave up and went to the store for 2 hours to straighten it out)
I was exasperated!
Content modified as required by Verizon Wireless Terms of Service
Thank you for bringing this to our attention.
In the future when activating a new phone on a number with an iPhone, the first iPhone must be powered off completely during the activation process. This can also be accomplished by powering of the old phone, then restarting the new phone.