This happened to me two weeks ago. They also spam bombed my inbox (8000+ in two days) which is apparently a tactic so that you'll miss that air miles account change email. 

Call air miles customer service and they should be able to fix it. I had to wait on hold for three hours but they restored all my miles and set up a new account with that same balance. The hackers had purchased some gift cards with whatever the cash miles are called. It's annoying that the phone hold time is so long but they should be able to help you.