If you want to cancel the monthly subscription service of Kindle Unlimited, please follow the following steps:

1. Go to /mycd.

2. in settings, scroll down to Kindle Unlimited monthly subscription service settings.

3. choose to manage your membership.

4. under the management membership, choose to cancel the Kindle Unlimited monthly subscription service.

5. choose to terminate your membership on [date]. Your subscription rights are valid until the paid service ends.

if you choose automatic renewal when signing up for Kindle Unlimited monthly subscription service, your account will be automatically upgraded to automatic renewal subscription plan when the trial period expires. This date is the next billing date in the Kindle Unlimited monthly subscription service settings. Before this date, you still have access to the Kindle Unlimited subscription service e-book.

I specifically consulted Amazon customer service: the cancel button will only appear under point 4 above if the automatic renewal fee is paid with a credit card. If the account balance is paid by trial or other means, the fee will not be automatically renewed and deducted after the expiration, but there will be a prompt to tell whether the trial will be renewed or not.