Product: Credit card

I am very disappointed and feel cheated by the XXXX XXXX Credit Card which is run by XXXX XXXX. I hereby complain about wrongful business practices of AMEX by misinforming the customer. 
ISSUE : I had made a payment in full on my due date, XXXX XXXX for {$5400.00} on my credit card. I was baffled to see that there was {$27.00} late payment fee on XXXX XXXX. When I inquired, AMEX acknowledged that I had made payment on my due date and they took off the late payment charge. 
However, a few days later ( XXXX XXXX ), they put an interest fee of {$80.00}, saying that I had made a late payment. I was very annoyed, and I called them trying to explain the situation, and also mentioned about the earlier conversation, but AMEX wo n't listen and would not take off interest fee. 
First, if AMEX believes I was at fault, they should not have taken off the late payment fee. 
Second, by applying an interest fee on a late payment which as per the first point did not happen, AMEX is contradicting itself and cheating the customers. AMEX agreed to this inconsistency and tried to cover up by offering me XXXX bonus miles for my situation, which I do n't want to take because it is not my fault and it 's insulting to me. When I asked them to talk to superior, they said superior was n't available and promised to call me back within 24 hours, which never happened. 
Third, AMEX insisted that since Bank payment was received after Mountain Time of XXXX XXXX on XXXX XXXX, it was considered as late charge. However, there is no information like this when you are doing an online payment. Here is a screen shot of what a customer sees when he is doing an online payment Fourth, as soon as you pay by hitting " I agree '', button the webpage displays a message that payment has been received. It does not mention a Time zone based cutoff. 
Fifth, in the " Pay by Computer Terms & condition '', statement and there is no mention of this condition based on XXXX MST Time Zone. 
Sixth, I feel it is arbitrary on AMEX 's part to impose XXXX MST based cutoff ( which is mentioned nowhere ). That means any customer in California, paying the due at XXXX XXXX is defaulting without even knowing it. 
I felt helpless, depressed, cheated and mentally traumatized by such big credit card company and their horrible customer service and business practices ; hence I lodge a complaint here. 
AMEX is involved in wrongful business activity by not divulging the correct information its customer needs to know to avoid such financial charges. They display incorrect message of " payment received '', which as a customer I will understand that I have done my part. Their warning of " if we do not receive the minimum payment ... .by payment date of XX/XX/2016 '' message term is ambiguous, because of XXXX reasons, first, there is no mention of this based on XXXX XXXX MST Time Zone cut off including in the detailed " Pay by Computer Terms & condition '', and secondly as soon as you pay by hitting " I agree '', button the webpage displays a message that payment has been received. 
AMEX must have earned a lot of money by sneaking wrongful financial charges in the customer 's bill and customers might have been unaware of it. I would like you to ask AMEX to take off this wrongful financial charge from my credit card and ask AMEX to improve its business activities by transparently displaying full information and detailing any impact when a customer is doing their payments.