I hired an individual freelance writer (he has no website, just an email account) on October 2016. The writer delivered a plagiarised work and I paid the money anyway. Three days ago, He emailed me threatening me of contacting my university and telling them about me unless I pay him money.

I paid him for three orders. Each one is 180 dollars. The last order was totally plagiarised but I discovered that after I paid him. I asked to redo the work and did not reply and then stalled for three months. After that, I stopped contacting him. A couple of months ago, he contacted me saying that he wants to help me with other work and I told no because he is a cheat and stole my money. Then I stopped replying to his messages. Three days ago, He emailed twice. This is his message:

"Hi, you have since refused to email. I am sending your contact and the dissertation topic and document to your college asap. I sent you an email long time ago and you still refused to email back. So I am sending the document, your contacts, email address, the document I did for you as well as the emails we exchanged to your college by end of today should I fail to get a reply from you from my other email address at gmail. Even if you had graduated that degree will be revoked and dont blame me for it."

What should I do? Please help.