If you want to stop using your Bitrix24 account with a commercial subscription, you'll need to disable the automatic subscription renewal option inside your Bitrix24 Cloud account.
To do this, go to Subscription > Purchase History > click Cancel subscription.
By default, the Purchase History page is available only to the account administrators. Other users will have access to this page if the Enable all users to upgrade current Bitrix24 plan option is enabled in your account settings.
Read more in the article - Automatic Renewals and Balance Top-Up.
Automatic subscription renewal is not applicable if you have purchased a commercial subscription directly from a Bitrix Partner in your region. You should inform your Bitrix24 Partner that you don't want to renew your commercial plan at least one week before the subscription expiration date.
All requests for cancellations and refunds are subject to the Bitrix24 Terms of Service.