Is this really a cancellation fee or is it just honoring your contract? AFAIK it's very clear on Adobe's page that your options are (1) Annual plan paid monthly, (2) Annual plan prepaid, and depending on the product (3) Monthly plan at usually 150% higher price.
https://www.adobe.com/creativecloud/plans.html
If you signed up for a yearly plan paid monthly, the cancellation fee is finishing your contract.
If you didn't want to agree to pay by the year maybe you shouldn't have signed up for a year of service?