If you're an Android user and have paid the one-time charge for the month or year, simply allow the subscription to expire. These charges are
set as a "pay per use" or "pay as you go" subscriptions. If for some reason you have been charged for the service without your consent,
please check with Google to make sure there are no settings which are set for recurring charges. For any billing issues or refund requests, please contact Google for further assistance.
Current Page for Google Refunds and Policies - https://support.google.com/googleplay/answer/2479637?p=play_refund&hl=en&rd=1
Request refund through Google Support - https://support.google.com/googleplay/answer/1050566