Work 365 has multiple types of Subscriptions

Note: Deleting a subscription that is synced with the Partner Center or an integrated provider should not be done through this process. This process is recommended for UAT Dev environments only. Refer to this article on deactivating a subscription for production environments. 

Subscriptions are provisioned from a Provider. There are three generic Provider  types in the System. This article will cover the deletion process for Manual, And Do Nothing Providers.

To permanently delete a Subscription that is provisioned as a Do Nothing or Manual Provider: