Mobile network

This is not a chat service, and is not a way to communicate directly with Apple; it is a user-to-user technical support forum. If you have a question or issue that you think another user can help you with please describe it in as much detail as you can and a user who sees your request and thinks they can help will answer, but that might not be immediate; it could be hours or days later. 

If you want to contact Apple use the Get Support link at the top of this page or call Apple by choosing a number from this list→Contact Apple for support and service - Apple Support

Here is some guidance on how to get the most out of ASC→Writing an effective Apple Support Communities post

To address your problem: Go to Settings/General/About and look at Modem Firmware. Is the entry blank? If it is you need to reinstall it by restoring the phone to factory settings, then restoring a backup. Back up the phone first, of course:

1. How to back up your iPhone, iPad, and iPod touch - Apple Support
2. Restore your iPhone, iPad, or iPod to factory settings - Apple Support - follow the instructions to restore using your computer, do not using Settings/General/Reset (which is not included in those instructions)
3. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

If the modem firmware DOES have a value you may have a hardware problem. The first step is what I just posted, but after that you need to contact Apple support using the Get Support link at the top of this page.