Ex boyfriend harassing and blackmailing

My ex boyfriend has been harassing me through texts and calls for nine months.I have blocked his number but he calls me from different numbers everytime.He has my parents number and so he calls them also. He is saying that he will tell about my past relationship with my other boyfriends and about being intimate to my parents.He calls one of my classmate every now and then and it has caused so many problems , he won't just stop calling me,my parents and my classmate.He threatens me that his mom will call my mom and tell her everything and then I'll be dead after that.I thought of complaining to the police but this will involve my parents and I don't want my parents to know about my past relationships and being physically active. This has to stop ,because this is creating so many problems. I stay in fear everyday that my parents will come to know about my past and this has created so many problems.I come from a very repituated family.