I can't install new software on my IPhone 7 because an error message comes in apple ITunes up that reads: ...can't be updated because activation info can't be obtained from the device. The phone says "unable to activate. An update is required.

My daughter's IPhone 7 received an update and shortly afterward the Cellular update failed. The phone couldn't send or receive calls and showed "no service." It intermittently connected for a day or so, then disconnected with the same issue. I tried reinstalling the software from ITunes, but it says it is unable to update because activation info can't be obtained from the device. The phone gets an error message in the set up process that reads, "Unable to Activate. An update is required to activate your IPhone. Learn more at apple.com/support."

Any ideas!?!