The Public Preview program for Office 365 did not include access to support. If you need help with this process you are encouraged to use the Office 365 community forum here: http://community.office365.com/en-us/forums/default.aspx
Not all tenants are eligible. For the "disable subscription" button to appear the tenant must meet certain criteria:
(1) Must show Office 365 Preview at the top left.
(2) Must have only one subscription and it must not be already deprovisioned.
(3) The subscription must be one of the Public Preview offers such as "Microsoft Office 365 Enterprise Preview" or "Microsoft Office 365 Small Business Premium Preview". The full list is below.
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