We try to prevent these unexpected charges by sending both a push notification and an email reminder to our users two days before their free trial period ends.
Since the subscription and payment management is handled by the respective app store you need to request a refund directly with Apple or Google.
iOS
To request a refund from Apple follow the instructions on this link: https://support.apple.com/en-us/HT204084
Android
To request a refund on Google Play please follow the instructions here: https://support.google.com/googleplay/answer/2479637?sjid=11322021814815747728-EU