Blackmail Scammed? Go here: https://www.scamsurvivors.com/blackmail/#/
This link takes you to everything you want to know about blackmail scams/sextortion. Also there you will see a scammer details form, so you can help warn others about the scammer. Please fill it out, and then you will receive the detailed steps need to protect yourself and others from the scammer.
Yes, change your number, and delete your snapchat account, too, along with everything else for a month.
Then, he should have real trouble finding you, and will most likely just give up.