Please note that because you subscribed to your account through iTunes, Apple's policy requires that you cancel and refund through them directly as well.
- Visit https://reportaproblem.apple.com/ (Login required)
- Sign in using the same Apple ID you used to purchase your subscription
- Search for the product and click on the button "Report a Problem"
- Select the appropriate option in the "Choose Problem" drop-down menu
- In the text box, enter your request for a refund and your reason
- Tap Submit.
Please make sure you have canceled the auto-renewal on your Premium subscription in iTunes before requesting a refund.