Uber jacking your bank account

So I get a mail from Uber SA saying that I have a pass for free delivery. Yay! I don't want to order from Uber though, but thanks for the thoughts. On closer inspection, my account is debited for R50 as the promotion is for free delivery for an order over R40. Remember I didn't order anything. So Uber deducts form my account just in case I want to order anything? What if that R50 was the last cash in my account that I needed this weekend?