How Can I Request a Refund for an Unused Subscription Charged Automatically After Trial?

I logged back into my account for the first time in a while. It signed me up for a 7-day trial and just charged me without notification on the 21st. I canceled the account this morning as I'm not getting enough use of the tool right now. How do I request a refund for the month of service I was charged but will not be using?