The subscription for the app is either through Google Play or Apple directly, so you need to cancel it first yourself.
How to cancel on Apple - https://support.apple.com/en-gb/HT202039
How to cancel on Android - https://support.google.com/googleplay/answer/7018481?hl=en-GB&co=GENIE.Platform%3DAndroid
Then for the refund:
Android: please can you request a refund here (https://support.google.com/googleplay/workflow/9813244?hl=en-GB)
iOS: please can you request a refund here (https://support.apple.com/en-gb/HT204084)?