How do I get this former classmate to stop contacting me after 6 years?

The year I graduated high school a guy who was one year my senior messaged me. We graduated at the same school but we had never talked. He seemed nice enough when we first started talking so I messaged him back and forth a couple times. Then a couple days into he confessed to me.

He told me that I was the only person who had ever been kind to him in high school and that I was beautiful, he loved my personality, I was his soulmate and the one made for him. Once again, I had NEVER spoken to him before.

I kindly said no thanks. But he continued on so I eventually unfriended and blocked him. Every couple years he’d try to refriend me on a different account. That went on until last year when I fully disabled receiving friend requests.

And now today on my instagram where we have no mutuals and my name isn’t even the same he has popped up and tried to friend request me.

6 years.

Its been 6 years of this.

How do I get this former classmate to stop contacting me after 6 years?
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