Charged After Cancelling Free Musescore Pro Trial Minutes After Signing Up

I made a pro account to print some sheet music for my fellow classmates in parts as opposed to a full score, and the minute I finished I unsubscribed from Musescore Pro. I check my banking statement now, a few days later, and I've been charged with $1.12. Although not much, no money should have been taken from my account. Why was I charged, and how can I assure I'm not charged again?