disgusting service new cell phone does not. work

I did an upgrade on one of my existing contract on the 2nd of July 2015 at Cell C store in Gateway mall, the said device stopped working on the 9th July 2015 and the store sent it for repairs an refuse to replace the device. I fetched the device after repairs on the 28th July 2015. Only for it to stop working again today. No loan phone was issued to me and no explanation given regarding the first repair. I am really frustrated with frustrated with the service of cell c and I would like this device to be replaced instead of being repaired again!