Disgusting treatmen Pep Stores Winkelspruit

Bought a phone at Pep Stores Winkelspruit on 22 June 2018 the new phone switches on and off. It does not charge and downloads games by itself. I went back 29 June 2018 to get a new phone. They refused to give me a new phone. I was in the 7 day period. I was told that I was suppose to bring the phone back by the same time I purchased the phone on 22 June 2018. Their service was disgusting and I got treated very bad. I now sit with a so called brand new phone that does not work. The make of the phone is Cell C wiz. What do I do now?