How to stop sexual harassment by teacher? I'm a student in India.  My music teacher was kicked out of the school about 1 month ago due to sexual misconduct. 

Today, he messaged me on Instagram with a fake ID and started talking nastily to me so I blocked him. He again messaged me with a new ID and asked for pictures and so on. I had to block him 3 more times.

He again messaged with a new ID of a girl. 
I gullibly replyed to the message but again he asked for pictures and some sexual chats so I blocked him once more.

This is not ending. He was my teacher and this attitude of his is not good. 

What should I do to stop him doing this?
And to prevent many girls from getting affected by this teacher?
I suggest you should report it directly to the police.

Why, well, as he has been dismissed from the school they have no control over him, so reporting it to the school will only be for information.

You can choose to tell or not your parents but you may value their support.

I hope this sorts itself out. Best wishes.