Subscription and payments are handled through Apple. Only Apple can process refunds for purchases made through an Apple iTunes account.
You can contact Apple Customer Support. When you get to this page, click Billing & Subscriptions followed by Subscriptions & Purchases. Once here, you'll be given a variety of avenues through which you can contact Apple.
We also recommend that you cancel your subscription to prevent being charged again next cycle. To do so, you'll just need to turn off auto-renew within your phone's iTunes account settings. You can follow the instructions from Apple.
If you are facing difficulty in using or observing an issue, then please report the same with details. So we can provide support. Our engineering team is spread across geographies to keep the app and VPN services bug-free.