Failure to access network on my Note 2 N7100

A

AC Question

I have a Samsung Note 2 N7100, i cannot access my local gsm servive provider it is advising me not registered to a network. I have resort the factory settings nothing happened, it gave an error message stating i should upgrade the software when i tried to do that it gave me a message that the device has been modified no software uodates. the OS on the phone is 4.1.2 please assist.