Product: Credit card or prepaid card

I have been in a dispute with American Express since XX/XX/2016 I went to use the card at an XXXX for about {$2000.00}. Although the card was up to date in payments, and the charge would not have put me over the credit limit, the card was declined. I used another card to purchase the material and later, received a text message from American Express asking if I used my card. This was after I had left the store. About two hours later, I received a message on my lap top, then about five hours after the denial, I received a prerecorded call. 
When I tried to contact American Express Customer Service I was routed to outsourced employees in XXXX. They did not have access to records that I needed for them to solve the situation. I was told that redialing the customer service may get me to an American Customer service representative because they had more access to the needed information.I was told by the outsourced customer representation that it was like " the lottery '' to get an American representative and he could not connect me internally. 
I then choose to correspond with the CEO of American Express. Each month I would send my payment attached to a letter. I would send these through the postal service Return receipt and certified mail to ensure the mailing an payment was received, Each letter included a check for payment and the amount of money owed, according to my calculations, although the receipts showed that the letter was received by American Express before the due date, the company intentionally held the check so that they could charge the {$27.00}, or {$37.00} late fee. This holding of the payment also had a negative effect on my credit score. 
American Express has several people contact me by phone and had one representative who promised to work with me to settle the matter. She made one call to me and I could never speak to her when I called. Therefore, I continued to send the payments through the mail to the Corporate Headquarters. This has continued and each letter shows my disputed amount. American Express has credited my account about {$500.00} and stated they were in error on parts but we are about {$1000.00} apart on what is currently owed. American Express has never replied on charges that I claimed were not made by me. 
Recently, while American Express had a {$150.00} payment of mine, they had their collections department contact a neighbor of mine who lives at the same address in a separate apartment. The representative asked for my number and told the neighbor that they were attempting to collect a debt. This person is not on my contact information that American Express has, nor is she related to me in any way. The person who made the call was contacted by me and told me he had every right to contact the person to collect a debt. He refused to let me speak to his supervisor, he did give me his employee number. I sent this information to American Express Corporate Headquarters though the U.S. postal service Express Mail. The return receipt indicate that it was received the Monday following the incident. No reply from the corporation has happened. 
Currently, I am drafting another correspondence to the Corporate Headquarters that I will send with this letter as an attachment.