You probably did this when you tried the flat iron method, but you're suppose to apply lotion (un scented, but I use scented that you can wash right off), and flat iron with the lotion on so it doesn't fry or melt or dry the hair.
I've done this on older g4's, and works like wonders, which is most likely different hair quality/ brand, but hey I tried!
(I made a video on this in case ya want to see it!-
https://youtu.be/IjiLO7LYjGY )
Good luck!