iPhone7 Service/LTE dissapear completely

Recently I have been having issued with my service and data on the iPhone7. I have the current OS and I have tried many if not all of the options in regards to "No Service" errors but in m case I end up losing everything up in the left corner. This seems to happen most when switching off wifi or when acceccing certain apps. Not really sure what the problem is, dunno if anyone has or had similar issues.