Delete and ignore, and don't waste your time wondering "why" he contacted you. It really doesn't matter.
Considering his behavior when you broke up, politeness from you isn't required. Be careful....showing up at your door again might be his next move. I hope not, but just tell him if he doesn't get out you'll call the police. He sounds like he has a loose screw.
You don't want to get back on that merry-go-round. BTDT.