Synchrony Bank In behalf of Amazon Exorbitant late fees w/o late notice Orlando Florida

As an Amazon customer, I was offered to open an acct. to what is called a "Store Card" which I accepted. I hardly used it except to take advantage of the initial offer which was a "one time discount" on the first purchase which was soon paid for.   After a long time of no activity, I received an email from this bank saying that I owed them $12.00.   I called them to question the charge and the told me that I had a charge of $5.32 from a Nov 12 purchase (which, after checking my Amazon Acct, I had no record or recollection of making) plus a $7.00 late fee.   I then told the agent that I never received a notice prior to the late asseslment and it was unfair on their part. A the end of our conversation the agent agreed to remove the cahrges w/o an argument or explanation; however this means that, had I never contested this charge, I would have been hit with it. How many times do they do this on the course of a day, and to how many folks that perhaps are too busy to catch this ripoff. This fee is unconscionable! in terms of an interest rate, it represents a rate equal to approximately 120% monthly rate. .......can this be now be legally allowed in America?  we've just lost all sence of honesty and fairness in this country; shame!!