IPhone ******** mobile

on the 13th of November 2015 I bought a certified pre owned I phone 5s from the I store in Cresta Mall, the phone was working in perfect order till the 5th of December the mobile stopped functioning and was searching for network at first I was unaware as to what was happening, I then went on the internet to find out what I could do to fix this, I consulted these sites [URL Removed] After restarting, taking my sim in and out and going on carrier setting, the mobile subsequently worked before it reverted back to searching for network again, from the sites that I had consulted there were lots of consumers who had experienced the same problem, so I thought to myself let me give it 1-2 days to see if the problem would resolve by itself. Falling to resolve the problem, I then asked my mother to take it back to the iStore in Cresta where I had bought it, the consultant that was assisting my mother as I was told by my mother checked the mobile and came up to a conclusion the mobile was broken and they will replace it, now they water damage and I must pay R 5068.41 ********