NO LTE COVERAGE ON HEADSET

MY SAMSUNG GALAXY S6 HAS BEEN IN FOR REPAIRS TO VODACOM 3 TIMES BECAUSE IT KEEPS ON THROWING ME OFF THE NETWORK, SAYING I AM NOT REGISTERED ON THE NETWORK, EMERGENCY CALLS ONLY OR THAT IT IS UNABLE TO CONNECT TO THE NETWORK. IT WORKS FINE ON WI FI. I AM NOT NEAR A SAMSUNG SERVICE CENTRE AND WOULD LIKE MY PHONE REPLACED EITHER BY SAMSUNG OR VODACOM. I HAVE LOGGED 4 COMPLAINTS ON THIS SITE TO VODACOM OF WHICH NOTHING CAME. SAMSUNG ADVISES ME TO TAKE THE PHONE IN FOR ASSESMENT, REALLY A FOURTH TIME?