If Amazon is unable/unwilling to do the right thing and refund you the charges, you are well within your rights to dispute the charges with either your bank (if the charge was to a debit card) or your credit card company.

You gave Amazon authorization only for a specific charge at a specific time, but they assessed you with a charge different from what you had authorized at a time that you did not authorize. You have also clearly done your due diligence with Amazon in requesting a refund for the unauthorized charge(s). It should be quite easy to file dispute with your credit card company.

If the charge was to a debit card, you have many rights under Regulation E, the Electronic Funds Transfer Act (I was in banking for 15+ years in my prior life). Your situation sounds like it meets Reg E's definition of Unauthorized Funds Transfer: an EFT from a consumer’s account initiated by a person other than the consumer without authority to initiate the transfer and from which the consumer receives no benefit. In my opinion, "from which the consumer receives no benefit" is the key part of that definition for you.

There are timing requirements that affect the dollar amount of your liability, so I would recommend contacting your bank sooner rather than later. At the bank where I used to work, the form we used for situations like this was an Affidavit of Non-Fraudulent Use (fraudulent use is when your card is stolen), and the reason that would apply to your situation was "amount different than authorized." You will have to provide your bank with information about the situation, because an affidavit is a legal document, but providing the info from all of your seller support cases should be sufficient.