Hiya, I changed my billing plan with a support agent from the 23rd of the month to the 1st of the month. We had to cancel and re-subscribe manually. I had Adobe Stock credits on my account which I lost during this process. [Moderator deleted part of this message for OPs protection]
Watning: 1. this is not tech support/customer service
2. customer service will not contact you
3. SCAMMERS MAY CONTACT YOU - this happens all the time
You must go back to a support agent. However, in cancelling you may have lost your credits forever, since there is no normal way to change billing date.
The only way to get this corrected is to contact Adobe support.
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! If the chat window fails to open, or is non-responsive, use a different device to start the interaction.
Support phone numbers may be found here: https://helpx.adobe.com/contact/phone.html. Please note that phone charges may apply.
(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here