I have installed at least 6 flashlight apps and NONE work.

You don't need a separate app. Swipe left to right on lockscreen, tap the plus sign to add widgets, select flashlight from the list. From then on, just swipe left to right on lockscreen to get the flashlight. Swipe right again to add additional widgets.

Simply install a flashlight app from Google Play to turn on your flashlight whenever you need it. There's a lot off free flashlight app from Google Play.