Is their any "holy" way on to getting rid of stubborn stress acne?

No there isn't any holy way lol But you can start by washing your face often. Plus you said that after covering your full forehead you got acne, that will only happen if you wear the same hijab and sweat a lot or have kinda oily skin. What you can do is either take your mom's advice or just wash your hijabs after using them. Nothing hard :) Good luck!