Edgars customer complain

On the 9th of July 2020, I bought a Samsung A21s at Edgars in Hazyview. The phone only worked for two weeks then it switched off, it was booked for repair then came back after 21 days a d only worked for three days then again went off. I demanded that they exchange the phone fir me as it had the same technical problem and do not trust that it will work again, it's already four months now I still do not have a phone. The store manager promised to help till this very day he hasn't come back to me. Now what steps should I take before I can get a new phone? What more reason does the store need before I can get it or how long should I wait?