You can manage your subscriptions on the channel you used for purchasing.
For subscriptions purchased through Google Play Store: Subscriptions can be managed from the Menu>Subscriptions page after signin in via the following link https://play.google.com/store/account/subscriptions
For subscriptions purchased through Apple Store: Subscriptions can be managed by tapping the "Manage your subscriptions" button after signing in via the following link https://support.apple.com/en-us/HT202039
For subscriptions purchased through website: Subscriptions can be managed by following the steps below after signing in via this link https://premium.getcontact.com"Profile page> Payments & Subscriptions > Manage Subscription Plan"
Please note that you can continue using your limits available in your plan, during the period you have paid for, even after you cancel your subscription. When a subscription is cancelled, fees paid for the previous subscription periods will not be refunded and in subscriptions cancelled before the billing cycle begins again, fees for the remaining periods will not be refunded.