If payement processing is under way, the cancelation is not possible. Also, if I remember well, it may take up to 24h before you can cancel a freshly ordered trial.
You can anytime contact Adobe customer support for more information on this. Adobe customer care can be contacted here: https://helpx.adobe.com/contact.html - click the small callout at the lower right of the screen and type "agent".
Regards, Abambo Hard- and Software Engineer and Photographer.