Harassment and intimidatiom

My 15 yr old child..playfully wrote "Allah ho Akbar" with fingertips on accumulated dust of a car parked outside of CHS. No scratches or permanent marks. The chs members are calling me and harassing me that they will file an fir for disturbing religious harmony! I apologised and told them it was a child s playfulness. Most ironicalky we are HINDU Still the chs members are harassing and intimidating My child is petrified Plz help