Few things come to mind.
#1 how did you treat with the poultry dust?
Best thing I found for applying is small powder bottle(baby powder type) I make my own using a small Gatorade bottle and punching/drilling several small holes in the cap.
To apply to chicken you separate feathers at the vent and give a good puff.
Next lift each wing, where the wing meets the body give another good puff.
Next separate feathers behind the neck and shoulders apply a puff there also.
Application completed, apply a 2nd treatment in 7-10 day.
Also this rooster might have some other underlying issues that makes him have poor hygiene for lack of a better word. If he doesn’t regularly take care of himself he will likely get lice again and again.
If he has/had lice you should treat the whole flock.
Hope this helps. Good luck