Sony Z1 defective screen - sony uncoperative

I have a Sony Xperia Z1. It is a great product, but unfortunately mine has a minor issue which won't go away. A yellow screen discolouration keeps appearing on the left hand edge of the screen. I contacted Sony who gave me the contact details of the authorised Sony repair shop, SSS cellular.I sent my phone in and after quite a while, it was repaired, SSS cellular informed me that there was a problem with the screen and replaced it. I would like it noted that this whole procedure cost me R 500,00 to get the phone couriered there and back. So now, we are 7 months on and unfortunately the same problem has come back. I contacted Sony SA who told me I would need to send it once again back to SSS cellular to get repaired. What are we going to do if this happens again and again. I am not prepared to keep paying for the courier costs, especially since the phone has been repaired once before and it seems there is a serious fault. Sony are unwilling to address the problem. I get out-mated emails telling me to send the product in again, they are missing the point, this is your problem, not mine. I have contacted the papers and [URL Removed] In my opinion this is terrible costumer service.