To cancel a subscription, go to settings for your profile: The user icon at the far right of the channel menu, then click on "My purchases" - "Subscriptions".
There you will see your active subscriptions under, and you can then click "Unsubscribe" from the one you want to cancel.
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