I am using Samsung Galaxy Chat B5330 (officially upgraded from 4.0.4 to 4.1.2). It used to work fine, but since a few days I am not able to call or send sms or use any network related services. It gives me error : "Not Registered On Network". I tried applying manual network settings. At first it gives a pop up : "Registered on Network". But as soon as I try to make a call, the same error : "Not Registered On Network".

I thought that factory reset would have been the solution to my problem, but unexpectedly , this too did not work for me. Please help.