D.D.
Reply with the words 'Stop texting me. I don't want to have any contact with you.' If he calls and you answer hang right up. Note the number and let it roll to voice mail after that. Save all the voice mails. If he continues go to the police and give them the entire history of this relationship letting them know you are in fear of this person doing something to injury you and your children. They'll probably tell you to get a restraining order and you should.
I know you want to set his straight on the lies he is spewing but don't. He's not in his normal brain with normal thoughts. The drugs has removed the ability to think so nothing you can say is going to make him realize he's being a jerk. Just continue to focus on yourself and your children. Don't give him any of your time and attention. Not worth it.