As Darthwraith mentioned, the way to report them is via right-click-report. Be sure to tag them as cheating if you suspect someone of being a bot.
Something to understand though, a lot of these accounts are compromised accounts. These actually end up costing Blizz money, not making them money. Their “subscriptions” are often tied to fake or stolen credit cards which then costs Blizz even more to deal with.
Unfortunately, botting will always happen in an online and competitive environment. Every time a company like Blizzard finds a way to squash a bot, someone makes a newer and better one to avoid detection.
Best thing we can do is report every one we see to help keep their numbers to a minimum!