Charged 260$ in Amazon AWS Free Tier RDS after 9 days. How come?

9 days ago we set up our web site in Amazon AWS taking advantage of the one year Free Web Tier.

Today we got a pretty unpleasant surprise. We have a pending billing fo 245$ for 7 days in September + 20$ for 2 days in October for the RDS MySQL service.

We configured the MySQL database installing it via yum, following the instructions located here.

How come is this possible? We had to cancel the account right away. It's shocking how we were charged such a high amount for a MySQL small traffic, small space DB. They have charged us the highest rate (0.74$ per hour)!!! Is there a possibility they will cancel that billing?

We are so dissapointed on Amazon. We never got any alert while configuring the instance, despite the absurd amount they were going to charge. At that rate a month would be 833$!!!