Refund Request for Unwanted Subscription Renewal

I recently noticed that my card was charged for a yearly Algomonster subscription. I have not used the application for a long time and was not aware that there was an active automatic renewal or standing instruction on my account. My intention was to purchase access for only one year.

Because of this, the charge came as a surprise. I cancelled my subscription as soon as I noticed the charge, but this only cancels the next billing period and does not issue a refund for the current charge.

How can I get a refund and cancel my subscription immediately?

Thanks.