Bad repair done,want me to pay for their mistake

I had my S4 screen replaced by Samsung as per the warranty, when I got it back the screen kept flickering. I called to complain and was told to return it and they will fix it. When I returned it i was told it will be done in 3-5 days, its 2 weeks now, I call 5 of the numbers they provided and none go through. I emailed the consultant who helped me(Catherine) and she didn't bother to reply. After I finally got through after spending hours trying, they promised to call me back many times. Its almost 3 weeks, now they start to fix the phone and want me to pay R1200. I just want my phone in the condition it was when I sent it with a new screen. I'm not paying a cent for your technicians terrible workmanship. Deliver my phone its almost 3 weeks. The job number is:SE125712. I'm due for an upgrade and meant to take an S6 edge, with this terrible service I never will, Apple I Phone is the way to go!