I cancelled my membership within 14 days, how can I get a refund?

I subscribed for a 7-day free trial plan a week ago and cancelled the membership 2 days ago, so before the end of the trial. I also immediately received an email confirming my cancellation.  However, today I received a notification from my bank account saying that I paid €8,12 for a monthly subscription. I just cancelled my membership once again, so within 14 days from the payment. How can I get a refund?