Cell phone purchase - Consumer Complaint for PEP STORES

I bought a Hisense phone from Forest Hill Pep store and when I got home the phone did not switch on. I returned the phone the next day and ths store manager named Sibongile changed the phone battery and told me the phone was fine. Today 13 days later the phone does the same thing, I take it back and now the same store manager can't change it because it has been over 7 days and I have to wait 3 weeks for the phone to be fixed. I initially asked for the phone to be exchanged and was told it is now fine with the new battery but today they can't do the same thing of changing the battery.