You'll be able to manage this plan shortly

The message means that you are in a transition period. Waiting 24 hours may solve the issue, but it may well be that you got charged by then (that is one reason to put the account in a transition state). If that happenes, and you are in your 14 days of your paid subscription, you still can cancel free of charge and you will be refunded. 

If waiting is not an option, contact customer service. Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled, you need to accept cookies! If the chat window fails to open, or is non-responsive, use a different device and/or browser to start the interaction.

For support via Twitter:
https://twitter.com/AdobeCare

(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here
https://community.adobe.com/t5/account-payment-plan/how-to-contact-adobe-support/td-p/11843852)

Important: Adobe does NOT contact you unsolicited by e-mail or direct message. If you get contacted by direct message from a person, claiming to be an Adobe employee, look at that profile and look, if they bear the “Adobe Employee” marking under their name. Adobe support does not use Skype to give you support.
If in doubt, ask the forum.