Vodacom replacement refusal/delay

I am the only full time paediatric Neurologist in Durban and Kwazulu Natal. Hospitals, emergency departments and Doctors are dependent on me 24/7. My Samsung S5 mini switches off at night while being charged, freezes unexpectedly, does not allow messages to come through and then prevents out going calls with \not registered on the network". I have had it repaired once already (it is 3 months old). I have asked for URGENT assistance as this problem is very dangerous. I do not want the phone back and do not want another Samsung S5 mini. The Advance Repair Centre Call line are not helpful and I am not getting a response despite writing a letter explaining the dangers of this problem"