iPhone cannot be updated

Hello,

There is a problem with my iPhone that requires an update, but i tried to update it but it didn't work, i also used iTunes to update and it didn't work too. It shows a triangle with Exclamation mark that says no service, i cannot receive any calls or use my cellular data.

So i restored the whole phone as new, but it still shows the triangle symbol that says "Unable to Activate - An update it required to activate your iphone" then it says Shutdown. (i already have the backup on my laptop).

In general i need to update the phone but i cannot update it. what should i do?

i have iPhone X , version IOS 12.1