hi, i found you charge me 3.18$ without any reason ,please let me know why?

This is not Apple. This is a user forum. We are users just like yourself.

You will need to contact Apple Support: http://www.apple.com/support/contact/

Probably an auto-renewing subscription. Use this article to check and manage your subscriptions: http://support.apple.com/kb/ht4098

i had the same problem when i changed my billing info. What is happening ?? there's no record of charging me that on my history.

Contact iTunes support and ask them