Question [Q] Replace board?

Few weeks ago I did a firmware upgrade, the upgrade went smooth but no matter what, it doesn't register to my provider's network (I checked if my IMEI is blocked or fake [0049] and it's not). I still see the other networks when I'm scanning with the device.

I replaced the firmware with dozens of other firmwares, none of them let me connect. I tried few other SIMs, same results.

So I'm thinking about replacing the board, but the problem is that I cannot find which part of the hardware I should purchase. The main-board on all web site don't mention any Modem/Radio on them, and the best I could find was a SIM daughter board.

So my question: which part I should buy?