HTC One M8 doesn't read sim card after flashing ROM

My HTC One M8 got stuck on bootload shortly after I asked O2 to unlock it. The bootload said ***software status: modified***
After a lot of research, I came accross a tutorial to fix a soft bricked device via TWRP and managed to flash a new ROM on it. I choose Stock ROM's (Android 4.4.4 + HTC Sense 6.0 | Latest: 3.28.401.9)/ stock HTC system dump that I found on android-revolution HD website and everything went very smoothly.

So my M8 is now starting and working fine, BUT doesn't read sim cards. It doesn't tell me whether a sim card is inserted, and if I put my Vodafone Malta sim card in, nothing happens, no error of reading, nothing. (if was working fine after the unlock code was put in).
I also noticed that HTC SDK API level now says unknown. And under mobile data>Network mode where I don't see 4G anymore.

I've received OTA update but can't install them. I get the "We have determined that your phone may be running a modified version of its system software. For your protection, we cannot update your phone. Please revert your phone to the official HTC system software to update your phone. If you did not modify your system software or would like help reverting your system, please contact us via the support section at www . htc . com".

I thought that maybe installing a new ROM would be the solution and tried various RUU to no avail (159 error). I also tried using fastboot to flash 0P6BIMG_M8_UL_M60_SENSE70_MR_HTC_Europe_6.12.401.4 _Radio_1.29.214500021.12G_20.72.4196t.01_release_4 64360_signed.zip
But it failed with 42 Wrong Customer ID (wrong CID).
I tried to amend android-info.txt but 1/windows won't open the zip (I am on Windows 7) - 2/ 7zip will but won't let me copy or edit the file (unsupported compression method error).

I am very much a newbie and I am not very keen on going S-Off as yet and would like to have opinions on what my next move could be, staying S-On.

My main concern isn't the updates but the non reading of my sim card. That's the main thing I'd like to resolve (and I thought that flashing a new ROM could be the solution - correct me if I am wrong!)

here is a reading of my device:
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0000
(bootloader) version-baseband: 1.29.214500021.12G
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 6.13.206.5
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: SH4BNWM05707
(bootloader) imei: 357336065912575
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B10000
(bootloader) cidnum: O2___001
(bootloader) battery-status: good
(bootloader) battery-voltage: 0mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: 76df2b54
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0

Thanks in advance for any advice!