Track down your purchases
You can review all the recent purchases made on your Steam account by following the process below:
Follow the above advice and see if you can identify a purchase that matches the charge on your bank account.
Track down your receipt
You should have been sent an email for any purchases made on your Steam account.
The email will have been sent to the email address registered to your account and should explain when it was made, what it was for and which account the purchase was made on.
Review your email inbox and see if you can identify a purchase that matches the charge on your bank account.
I still don't recognise a charge
If you still aren't sure what you've been charged for you'll need to get in touch with Steam's payment team for further support.