[I cannot downgrade from "Premium - Annual" to "Basic Account".]

I am trying to downgrade from "Premium - Annual" to "Basic" account.  But, when I try to do so, the following error message is generated. --- To upgrade your account you must have a credit card on file.  I am not upgrading.  I am downgrading.  My annual membership was paid for a year ago and there is no payment is due in my account.  How can I change my membership plan to "Basic"?