Horrible service at Exact matlosana mall

I bought a phone on the 23rd of October and I experienced difficulties with it . On the 30th I went back to the store to return it. I was told that the only thing they can do is to book it for repairs even though that phone was new. The manager claimed that her staff members informed me that the 7 days has passed and I don't even have a witness to verify that I wasn't told about the 7days or even how is it counted. I felt so insulted and my rights as a customer have been violated. I was sold something that had problems and now the store tells me that they can't do anything about it the only thing is to repair. How do you repair something that is new?and why do I have to suffer the consequences of someone not doing their job correctly?