no service

I am Noel from Tamil Nadu. I am using 4s 6gb with latest os 8.4.1, last Monday suddenly my signal was lost and no service was shown in display.I thought something problem with my network but it was not i came to know problem is with my device. i tried everything like changing date,adjusting attena etc. But i couldn't make it. So i took to my phone to service center ,also there i got negative result it cant be rectified 😟 . Someone could help me on this.