If you can't get rid of bot players physically, at least, make it so that losing to AI bots gives you 0 XP or going 0/10+/0 gives you 0 XP. This will totally negate or slow down the progress of lvling up the botting accounts which in turn may have a higher likelihood of them getting banned before they reach 30.
People may say that its not fair to new players since if they lose or go 0/10+/0 to AI bots they won't get XP. To that I will say there is beginner bots.
Believe me when I say that losing to AI bots as 5 real players is much more educational (because AI bots are there for us to learn to play League) than losing because you were outnumbered.