To cancel your subscription you simply go to the app store you purchased from, view your subscriptions you currently have active and cancel from there.
Please see this support article from Apple with full instructions : https://support.apple.com/en-gb/HT202039
Please see this support article from Google with full instructions : https://support.google.com/googleplay/answer/7018481?co=GENIE.Platform%3DAndroid&hl=en
Please read the following carefully to determine how to get a refund and if you are eligible:
Upgraded via the Apple app:
If you upgraded through the Apple app, your charge was processed via iTunes. This means you'll need to request a refund through Apple iTunes. Unfortunately, we're unable to refund purchases made through iTunes, due to app store privacy policies.
You can contact Apple about a refund using the 'Report A Problem' link on your email receipt. More instructions here: https://support.apple.com/en-us/HT204084
Upgraded via the Android app:
If you upgraded through the Android app, your charge was processed via Google Play. If you request a refund within 48hrs of purchase, you might be eligible for a refund.
To do this please see this guide from Google : https://support.google.com/googleplay/answer/7205930
Please note we do not offer any refunds above and beyond Google Plays own policies.