When coming to cancel a subscriptions, it's important to note that all maters of payment management are handled directly by Google and in their console.
Therefore, if you would like to cancel your subscription and receive a refund, you must contact Google directly.
To contact Google:
1. Go to https://play.google.com/store/account and log-in with the user you used to purchase the application.
2. Find the application click on the icon on the right side of the Price column. Select "Report a Problem"
3. Select "I'd like to request a refund", add an explanation as to why you would like a refund and click on "Submit".
Now all you have to do is wait for Google to answer. They will respond by email to the address associated with the account.
Please note that the above relates to a product of a 3rd party, not being Applicaster. It is thus subject to change at any given time, according to the sole discretion of Google.
For further details on the Subscription cancellation process, please turn to the official documentation of Google on the matter: