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.
- Launch Settings on your device
- Select iTunes & App Store
- Select your Apple ID
- Tap View Apple ID from the pop-up window
- Enter your Apple ID password or fingerprint ID
- Tap Subscriptions
- Select your product
Please make sure you have canceled the auto-renewal on your Premium subscription in iTunes before requesting a refund.