Error message "no service available"
My son's iPhone (5S) has this "no service available" in the top left corner where the telecom-company should be stated. Found this Apple-Q&A where they say that I should update the iPhone software. I have now connected the iPhone to the laptop and when searching for updates I get the message that the iPhone has the latest software installed. What to do? Thanks for any help!
iPhone 5s, iOS 12