Auto-pay needs to be turned off at least one day before your due date to make sure it does not go through. If you turned it off on the day of your payment, it may have already been scheduled.
If you prefer to make manual payments, you can always pay early or on your due date before auto-pay processes. Just make sure your payment is made on time because missed payments may affect your access to features like MyPay® and SpotMe® and  and will be reported to the credit bureaus.