Warbex works fine but it is getting late to use it, due to the grubs getting killed while in the wrong place. Known of that happening, especially with Warbex. that is addressed in the first link I posted.
We had a Lewis Oiler the cattle used too, so that helped break the life cycle of the lice.
There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.