My ex harasses me online. I keep blocking his accounts but he keeps creating new ones and harassing me and telling me cruel and bad things about me that aren't true. How can I finally get this to stop?

That must be very disturbing for you, to get harassed all the time on online accounts. He is threatening you by telling cruel and bad things about you. You should keep record of all his texts and register FIR against him with police. He will get arrested or get warning from police. That is only one legal solution. And if you can't do that then if you are younger then talk to your parents or some elder person to whom you trust. If they can give him some warning to stop it. Or if you can't tell anyone then gather all courage to tell him directly that you will take legal action against him if it continues. Unless you raise your voice he will keep feeling more powerful to harass you.