My galaxy J7 is about 6 months old now and I have a problem where it gives not responding message to callers ( as if the phone is switched off or out of network reach) , even though the phone is switched on and SIM is active and mobile network is available. When I restart the phone it works again properly. This is happening most of the time on daily basis and very frustrating. Could this be a hardware issue? Appreciate if any of you could help to resolve this matter.