No Repair to in Warranty device with manuf. defect

in May 2014 i purchased a LG P713 (optimus L7 II) from the LG life style store in Canal Walk, the phone developed a small issue of the screen going blank when it got cold, but the problem went away i assumed it was no longer a problem, fast forward to March 2015 the same issue developed but even worse, so in April 2015 (5 days before my warranty ran out, stay far from them so its not always as easy as just popping into shop to return it) firstly the sales agent that helped me tried to refuse to take my phone stating they dont take out of warranty phones in for repair, so i produced my receipt and they eventually agreed to take the device, after 2 weeks of waiting they eventually phoned me saying it will cost me R1600 (on a device that cost me R2500) to repair the device by installing a new screen and digitizer, after i got the device back from them no fixed no proof that the phone was even looked at. at this point i found 2 other friends with the same device and the same issue also since day 1, so i posted on LG Mobile's facebook page and they commented asking for my details so they can contact me and relevant parties for investigation, that was almost 2 weeks ago and still nothing