The same thing happened to me a year ago. I had an AWS account I barely used except for an SQS queue. Somehow, someone got in, changed the password, and set up a machine learning pipeline. I couldn't turn it off since I was locked out of the account and I racked up a $20k bill.

I also have no idea how they got it. I had 2FA set up and only had one service key created that I used in a Heroku environment variable.

Here's what happened:

- I contacted customer service. It took them several days to get back to me. Initially they told me they couldn't help and I would be responsible for any charges per their ToS as it's my responsibility to secure the account.

- After some back and forth, they reset my account credentials (the email was changed from me@mycompany.com to uuid@random.ru so it was obviously an account takeover).

- They listed out a list of services that had been started after the compromise and told me it was my responsibility to disable them and then tell them I did so.

- I cleaned things up the best I could and then told the service agent. They said I missed a few things and gave me more clear directions.

- By this point I had a $70k bill. Things had been running for about a week.

- I asked about getting a refund and they said they could do that but only after I set my account up with a proper security setup, which involved creating a bunch of separate small user accounts with minimal permissions.

- I did that, they refunded the charges, and then I deleted my account.

Long story short, it took a while and they weren't initially too helpful but ended up being very nice and helpful in the end.