Faulty phone and bad service

My mum bought phone from pep home at Marble hall and that phone its faulty then tried to return it at groblersdal now they tell me to return it where we purchased it and that phone is only a R150 and goin back to Marble Hall will only cost me another phone and according to cashier i must return it within 7days so that i can get a new one...that is bad service because when you buy phone i didnt know that they selling reject staff that you will end up spending more for their own mistakes..