Iphone 6 Searching and No service

I have iphone 6 ..it was working fine but sometimes when i used to dial a call it drops signals and when i cut the call signals come back and some times it goes to no service and i had to open the iphone and disconnect battery and charging port connector many times to get the signals….but last week it was dropped 2 times very bad but still was working and within few days it came back to no service.. i thought it was amplifier problem because when i removed the shield it was in golden color so i tried to change the signal amplifier U_LBPAD ic but no luck !! any solution guys ?
NOTE: I can see IMEI and Baseband FIRMWARE in ABOUT but when i dial *#06* it does not show anything and code disappears…. please help guys !