Bad service

We purchased new screen protectors for iPhone at the istore in the East Rand Mall Boksburg. The casher battled to fit the screen and she asked assistance from the store Manager. After a long struggle they managed to fit it, the store manager advised my wife to not fit the cover now she must wait an hour. So, she fitted it the cover later the afternoon. The next day she noticed the screen was cracked and I took it back to the istore and request a replacement as there are no signs of any damages to the screen it is cracked for no reason. I confronted the store Manager regarding them battled to fit the screen and ask if they perhaps did not damage it then when the fitted it as they battled so long getting it right. I again requested that they must replace it free of charged. The rude store Manager bluntly refused to replace the screen. I am 100% convinced they damaged the screen when they battled to fit the screen, so much for customer service.