My Samsung S21 Ultra does not Work!!!!

I received a new Samsung S21 Ultra a few months ago on a contract from Vodacom. I have not been able to use it because from day one this cell phone has not worked properly. My wife and I got exactly the same phones together on the same day. She has had no problems. I have send my brand new phone in for repair 5 times. Every time they send it back saying there is nothing wrong with the phone. Everytime while I an on a call the phone it turns off completely. First I get cut off on the call, and then it switches off entirely. Sometimes it switches immediately, and this always with with a full battery. Neither Vodacom or Samsung are prepared to do anything about this. I continue paying a phone that does not work. What do I do now. The chap working at Vodacom repair center suggested I go to the consumer council. Neither Vodacom or Samsung want to take any responsibility to remedy this situation. What do I do now ? Legal Action ? This Phone has been faulty from day one!!!!