Problems with Cell Service and 4G LTE ever since updating iOS 11.2 on my iPhone 7 Global Edition, and in Restore mode after updating to 11.2.1

About one weeks ago, I downloaded and installed the iOS 11.2 update to my iPhone 7 Global Edition Model A1660. Ever since then, it's been struggling to connect to the Cellular network, and would often be stuck on "searching" or "no service". Today, after 2 weeks of this, I got fed up and tried to fix it. I tried everything, like resetting my carrier settings, re-inserting my SIM card, etc. The last thing I tried was to restore the phone. I backed up my phone on the iCloud and then erased and restored. When I rebooted my phone shortly after, I found that I still had no service or 4G LTE.

I then decides to update to 11.2.1 using ITune, ITune gives error(-1) and my iphone 7 Global Edition is now useless. It is always in restore mode.

I have tried to restore my Iphone 7 in Restore mode and DFU with Itune, and Itune always give the same error(-1).

I then bought Reiboot Pro for 29 USD and it cannot fix the issue.

I sent my Iphone 7 to a local Authorized Apple Service and Reseller in Viet Nam, the technical team has checked the hardware of my Iphone 7 and there is no problem at all. And they cannot updating my Iphone to IOS 11.2 or 11.2.1, and they are getting the same error(-1) while updating my Iphone 7 to IOS 11.2, 11.2.1

What should I do? My Iphone 7 global edition becomes useless after updating to IOS 11.2 and 11.2.1.

Please fix IOS 11.2, 11.2.1 for that it works with Iphone 7 Global Edition or provide a signed IOS 11.1.2 so that I can restore my Iphone to this old version.

To be honest, IOS 11.2, 11.2.1 is very bad, It is causing trouble to my work and my time