What to do if someone is blackmailing

Im in a big trouble i wnt help... i have a boyfriend who is my senior and we got breakup. One of my class boy is daily harassing me to talk daily otherwise i will tell everyone bad about you because of that fear i used to tlk with him sometimes if i won't talk means he will call everyone and ask them to give phone to me and they started to scold me thats why ill talk with him. Once he harassed me to say about all my persnoals with my boyfriend i told him he saved all those chats and blackmailing me. If anyone of my classmates will talk with me means he will talk soo badly abt me like how many boys you want and he will use so many bad words. He is having my mother's number now he is blackmailing me that i will spoil your future you have used me i will tell everything to your parents by showing those personal chats. Now i don't what to do . Plz i need your help.