Note: If you delete the app, it will not cancel the subscription!
Cancelling the subscription prevents you from the subsequent charges. However, that doesn't refund your last payment.
Please follow these instructions to cancel the subscription on your Android device:
Open the Play Market app on your Android device;
Make sure you've logged in to the correct Google account of yours;
Click the Menu icon -> Subscriptions;
Find the subscription you wish to cancel;
Click the Cancel button;
Follow the instructions in the Play Market.