I actually had a billing alert set, and I did get an alert, but it looked like this: "You are receiving this email because your estimated charges are greater

I actually had a billing alert set, and I did get an alert, but it looked like this: "You are receiving this email because your estimated charges are greater than the limit you set for the alarm "awsbilling-AWS-Service-Charges-total" in AWS Account XXXXXXXX. The alarm limit you set was $ 10.00 USD. Your total estimated charges accrued for this billing period are currently $ 1050.95 USD as of Saturday 18 July, 2015 17:34:36 UTC." So, it came a bit too late to take action.