What should I do if I've received a bill, but have already paid?

What should I do if I've received a bill, but have already paid?
If you have received a bill after you paid for your subscription, the bill and your payment probably crossed in the mail. If you want to check your account status at any time to verify that we have received your payment or if you feel that there has been an error in processing your payment, click here. Please provide any additional information to help resolve the problem.