Latest software update 15.6.1

The 15.6.1 contained only security patches.

Two channels of internet access.

Cellular:

Support article: If you see No Service or Searching on your iPhone or iPad - Apple Support

Go through the various suggestions in the support article above but if they don't help, and your network carrier can't help, then  contact Apple Support for further investigation. You should be able to reach them here

Contact - Official Apple Support

or phone numbers

Contact Apple for support and service - Apple Support

Wi-Fi:

If Wi-Fi will not connect 

·      Reset the router to factory settings (menu or paper clip)

·      On iphone Settings, General, Transfer iphone or reset, reset, reset network settings

·      If you have a VPN you are strongly recommended to uninstall it and its profile in Settings, General, VPN and device management 

Here's some more steps you can try for Wi-Fi connection issues that may be helpful if your phone will not connect to WiFi

If your iPhone, iPad or iPod touch won't connect to a Wi-Fi network – Apple Support (UK)