mobile

I'm about to send the tablet for a repair but just wanted to check that it isn't a software related issue.

So, tablet has been working perfectly for 2 years but I never used the 3G on it. Recently I installed a SIM card in it and here's what happened:
1. Absolutely nothing changed after the card was inserted after many restarts, switching off WiFi, Bluetooth and switching Aeroplane mode on and off in Android 4.4.4
2. Tried card in another phone and it was all fine
3. Tried a different SIM from a different network in tablet and again nothing
4. Tried to check mobile settings but the menu wasn't there! When I go to Settings, here are the menus listed under Wireless & networks:
Wi-Fi
Bluetooth
Data usage
... More
Aeroplane mode
NFC
Android Beam
VPN
5. Updated to Android 5.02 - still nothing but this time I could get to mobile settings by doing a search in Settings
6. Did factory reset + wipe cache in recovery mode
7. Tried to add APN manually but settings I fill aren't saved after I tap back or Save under 3 dots
8. Upgraded to 5.1. This time, when I search for mobile data, all the menu items are greyed out and can't select them
9. Checked for IMEI number in about / status but it does not exist

Not rooted but was a seller refurbished so don't know its entire history

Kernel:
3.1.10-gf57b8b
Build LMY47D
FCC MSQME370T

Is this a hardware fault?