Through some testings, it seems my router cant block MAC address with wired connection. I end up blocking all possible IP addresses with firewall, except for mine. Glad that works.
My router is actually at the common lounge and he had his PC set up there to plug to my router through a wire. While he wasnt at this PC this morning, i plugged out his internet cable and put a note on the router.
If he still insists on trying to steal my goddamn wifi, ill chop his balls.