iPhone 6+ Touch Screen Disease

I have an iPhone 6+ that i bought from the centurion store in 2015. Recently the phone showed some white bars at the top of the screen, which flicks at times. When this first started i had to do some research on the problem, only to find that it was something common with such models and the problem is called "Touch Screen Disease" see https://www.apple.com/support/iphone6plus-multitouch/ What surprises me is that no one seems to know about this problem at iStore, only to be told that if the devise is not insured, then i have to get a new one. I would have appreciated if someone explained to me that it is the problem that they cannot fix. How come Apple SA does not know the "Touch Screen Disease"?