My G7 does not receive mobile service signals.

I am using it for 5 months and encountered this problem many time from past 2 months, that some times suddenly signals dissapre and even after restarting it for many time and powering it off it does not work.Today I am upable to make or receive call since 2pm till now. No I tried to factory reset but still no luck.

Please help me with tghis, i still have a warranty.

Is it a service oporator's fault or a mobile phone fault.