I made a payment for my Jan. bill for my AMEX account early, on Dec. 28, assuming since I already made my payment for my Dec. bill, this Dec. 28 payment would go toward my Jan. bill. At the end of Jan., I discovered I was charged a late fee and my credit score immediately went down. When I called AMEX, they said the 28th of the month was the last day of my billing cycle for that month, so they applied the second payment made on Dec. 28 to my Dec. bill and not Jan. Therefore, my Jan. bill was considered "late-unpaid." They did ultimately refund the late fee back to me, however, and most importantly, it had already been reported to one of the credit reporting agencies, causing my credit score to go down by 12 points. This is absolutely unacceptable. AMEX stated if I paid my Jan. payment on Dec. 29, which is the first day of my Jan. billing cycle, it would have been credited toward my Jan. bill. How is the consumer supposed to know this? I was acting responsibly and making a payment early from my perspective, but now, my credit rating is permanently effected, as decreasing by 12 points when NO OTHER CHANGES ON MY ACCOUNT ACTIVITY anywhere had been detected. This is completely unacceptable and something should be done immediately to rectify the issue.