If you want to cancel your eyeson Premium subscription, you do not need to contact eyeson since you can do it easily on your own 😉.
As a first step, go to Settings:
Then, scroll down and tap on iTunes & App Store.
Now, tap on Apple ID:.... and then on View Apple ID.
Then, click on Subscriptions.
Now you have an overview of all your subscriptions. If you want to cancel the eyeson subscription, tap on the app and then on Cancel Subscription & Confirm it.