What would you do? How would you react? Should I be mad at my parents?

your son needs to tell u where he is going as long as he is still under ur roof. that was bad of him to make u worry. i would also be angry and let my parents know that helping him sneak out will only lead to other bad things in life. let them all know there needs to be better communication. u should tell them u don't mind if he visits but u need to know he is safe. and calling after he calls out is not acceptable. u r the mother take control of this.