damaged cell phone tablet

I bought a cell phone on the 16th of February at pep cell Jane Furse and the phone actually has a damage it cant pick up network and when i returned the phone they are telling me that u have to wait for 3 weeks for them to fix my phone so i have told them that the 7 days is not yet finished so the customer service says they have nothing to do with this matter and i should deal with the shop i really want this shop be closed because i'm sure i'm not gonna be the last person they are ever gonna do this to i want a new phone or my money back i do not have money to pay for damaged goods they should be responsible enough to leave someone in charge when they are not around i want my money back or a new phone.