How do deactivate my AWS services when I have a member account listed in the organization?

Organization cannot be deactivated when there is an active member account in the organization. The options are to open support case to regain root access and close the account. You can also attempt to close the account from the organization console if All-features are enabled.

https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_accounts_close.html