Amazon Prime Charged After Cancellation

I live in the United States and recently cancelled my Amazon Prime subscription about a week ago. Despite this, my bank has just informed me of a new charge of approximately $15 from Amazon, shown as an Amazon bill, which I did not expect after cancelling. I could not find a phone number to call Amazon customer service and therefore have not been able to clarify why this amount was taken from my account after cancellation. I believe this charge is incorrect or unauthorized, since I had already cancelled the service. I request that this $15 charge be reviewed and refunded to my account, and that my Amazon Prime membership or any related paid subscriptions be fully cancelled so that I am not charged again in the future.