A few minutes ago I received a mail. I doubled checked for sender and included links looking for a sign of scam, but the message appears to be legit. The mail body (bold is mine):
We periodically audit our metering and billing processes for accuracy. During a recent such audit, we found a rare case where an error condition could cause incomplete processing of a snapshot delete operation. This resulted in ongoing storage charges that were billed to your account. The issue has been resolved and all deletions have completed.
We are crediting your account 907093643858 USD for the previously billed storage of these snapshots.
Should you have any questions or concerns, you can contact the AWS Support Team at http://aws.amazon.com/support .
Oh my God!!! There was an error in the billing process, and I've been credited almost a trillion dollar on AWS!!!
But I've just found that
907093643858 is my account ID, the refund is just 8.24$, and AWS people are not able to format an email message.
Edit: just received another mail
Earlier today, we sent an email regarding a credit for RDS snapshot usage. This email included your account ID, but mistakenly left out the dollar amount of the credit. The credit for your account (907093643858) is $8.24 USD. We apologize for any confusion this caused.
Amazon Web Services
(Note: of course I've modified some figure of the account ID to mask my real one)