My friends like to laugh at me.

It is common to be laughed at by friends occasionally for doing ridiculous things. It's wrong to laugh at you often. When a friend insults you, it means that he doesn't actually treat you as a friend, but you treat him as a friend. Friends insult you without encouraging each other, which is not friendship at all.

He just regards you as his plaything and laughing stock, and doesn't have to answer his harassing phone calls at all. The most important thing is that you should build up your self-confidence. You are not a joke, you are a dignified person. You don't have to say anything to him. You don't want to talk to him. Ignore him.