I'm trying to avoid an ex crush but he won't leave me alone?

What am I suppose to do. Its bad enough that he's in my homeroom cl but he's in 3 of my cles out of 6 cles.Not including that he sits next to me in every one of them. He even tries to strike up a conversation. I've told him many times that I don't want to have any contact with him and all he does is laugh, I'm like what the hell? Why is he doing this? Does he think i'm joking or something? Because i'm pretty sure I made my point clear. So how am I supposed to avoid him when he's just "there". When is he going to get the message. Besides he said he didn't like me at all in fact he said and still says he "hates" me. So if he hates then why won't he leave me alone. Its kind of annoying.