Istore gateway mall are ******* and *****

My younger brother bought an Iphone 7+ 2 years ago and last year January it stopped working and he took it back to istore gateway mall where he bought the phone. Istore gateway mall told him the phone can’t be fixed and he must pay almost R8000 for another phone and he did, and didn’t get the damaged phone back, so the 11 months down the line in January 21 the so called new phone stopped working and he took it back to istore gateway wall and they told him they wont fix it since it had only 6 months warranty but on the phone papers is 12 months warranty. So we took it to wefix Pavalion mall, where they made us pay R200 to check the phone but refused to fix it and said the phone has been worked on before, which that gives me an impression that this phone was a CPO phone to begin with, why would they give 6 months warranty on a brand new phone which comes out new with a 12 months warranty? They took the first phone so I also think they fix old phones to sell them as new at a later stage. I want istore gateway mall to answer and also give back the phone they took in the beginning. We gave them proof of the purchase on time and we wanted istore to give us answers