No network connection

If you have lost cellular connectivity and have discussed this with your carrier, then perform the "no service" steps linked below, then contact Apple Support and discuss your options and alternatives. If the "no service" does not resolve this, use the Support link in the lower left corner of this webpage, and select Chat or Call, as and if available.

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

It connects to Wi-Fi OK but not cellular?

Are you using a physical SIM card or an eSIM?

If you look under Settings > General > VPN & Device Management, is anything listed there?