To cancel a subscription, go to settings for your profile: The user icon at the up right corner of the channel menu, then click on "My purchases" - "Subscriptions".
There you will see your active subscriptions, and by clicking on "Unsubscribe" you can cancel them.
Please note that if you do not see “Unsubscribe”, the subscription has been successfully ended and you will not be charged automatically anymore. Note that your subscription will still be active until the active period is over.
Address directly to that page: https://solidsport.com/user/profile/unlocked