Then you will report that to the bot owner. They will check if you really did send the bot money. The money transfer is a public transaction on the blockchain and easily verifiable as well as whether or not the bot upvoted your post. If it's a bug, the bot owner will fix the bug and you'll get your money with apologies. If not, people will stop using the bot once you complain about it in public.
You can try to contact the bot owner. Chances are you are screwed though. I have got a refund a couple times but some of those bots are straight up scam artists.