DAMAGED WITH IN SEVEN DAY PERIOD

Samsung core was bought about 4 months ago, within the 7 day period I started having problems with the phone. I took it back to Edgars Canal Walk where I originally bought it from. When I purchased the phone the Mr Jeffery told me if I have any problem with it they will replace it immediately, guess what , problems started within the 7 day period where they would exchange for a new phone. When I took it back to Edgars I was told he cannot exchange the phone as he has to send it away for repairs, which I queried as this was a brand new phone. I was then told to take the phone to Vodacom where they told me there was nothing wrong with the phone. SO MUCH FOR A SEVEN DAY PERIOD!!!! OVER PROMISED AND UNDER DELIVER