Hi, I haven’t cellular data

Start here: https://support.apple.com/en-us/HT201415

Is your cellular data turned on you can check by Clicking on the icon that looks like a tool, also know as Settings>Cellular Data>Slide the bottom at the top. All this is on, make sure your sims card is secure in the tray inside your iPhone. If all that is good and you are WiFi, enable WiFi calling and call your server provider.

See discussions.apple.com/thread/8562793 for a similar Q&A.

https://support.apple.com/en-us/HT208733