Sign up for Office 365
Learn more about Office 365
You can cancel Office 365 subscription online without penalty at any time, during or after the trial period. You can also open a service request from the administration portal (if it is an Enterprise tenant) and ask for the tenant to be decommissioned.
In addition, you may also contact our Sales and Subscription Team for further support they will provide you with more detailed information’s on this issue.
For more information about billing /cancel subscription plan: http://office.microsoft.com/en-us/help/contact-support-for-technical-presales-billing-and-subscription-issues-HA103836042.aspx,