Your Subscription is auto renewing. When you originally ordered, you selected PayPal OR standard Credit Card processing. Whichever method you selected, it was set as the default method for future subscription renewal payments. If, for any reason, paypal or the CC processor is unable to process a renewal payment, it will retry several more times. You will receive an email upon each retry failure. After the third retry fails, your membership will go on hold and your access will be restricted.
These are the steps to change/update your payment methods.