Step 1: Go to https://play.google.com/apps/publish/?account=5610482215473659924#OrderManagementPlace and log in if needed.
Step 2: Search for the user by email.
Step 3: Click on the latest Order ID to be taken to their account page:
Step 4A: To cancel a subscription click on the “Cancel Subscription” button. You will need to confirm the cancellation by clicking the "Submit" button in the pop-up.
Step 4B: To process a refund on Google Play, click the "Refund" button. In the pop-up enter the refund amount, provide a reason in the drop down, and then click "submit".
Step 5: Let the user know!