You can report bots, it's called 3rd party programs in the report box. Also calling someone out for being a bot wont always work, as sometimes they actually have someone at the computer watching, and they then speak up when you mention it so they "don't get caught." or they turn off the bot and actually play themself.
Someone actually went through an aram with everyone but him a bot. Any that was low stood on the health pack, because they were programmed to if they were low.
Also, Riot bans in waves to prevent botters from knowing what exactly gets them detected.
You will never be able to fully get rid of bots. If it was possible, pretty sure WoW and any other high-up their money-only mmo would be bottless by now.