Product: Credit card or prepaid card

I have had an Amazon Store Card ( ASC ) issued by Synchrony Bank ( SB ) since XXXX. From XXXX until the present, I have set things up so that my bank, a subsidiary of XXXX XXXX ( XXXX   ), through a service called XXXX, directly receives my monthly ASC bill and is instructed to automatically pay SB the full amount due on my ASC, thus reducing my account balance to XXXX  each month. This arrangement has been in place since XXXX and has never been changed. The arrangement worked as intended from XXXX until XX/XX/XXXX, when SB, without my knowledge or consent, began to deduct only the 'minimum amount due ' ( as specified on my monthly ASC bills ) each month. As a result, an unpaid balance began to build up in my ASC account, on which SB charged interest, per the cardholder agreement, at APRs of up to 25.99 %. I have had credit cards for over 40 years and never carried an unpaid balance or accrued interest charges ; I have certainly never instructed an issuer to only be paid the 'minimum amount due ' ; at all times I kept sufficient funds in my XXXX account, at ultra-low interest rates, to cover any possible balance on my ASC and other monthly bills. Having automated the payments on my ASC, I did not detect SB 's unauthorized actions until early XX/XX/XXXX, when I first complained to SB about the matter. XXXX  informed me that XXXX  is a third-party provider, and that XXXX  allows payees like SB to decide how to interpret my instructions and determine how much they will deduct from my account ; since SB has not disputed this information in four months worth of phone calls and correspondence, it is clear that SB ( rather than XXXX or XXXX XXXX made the decision to switch from deducting the full amount each month to deducting only the 'minimum amount due '. SB also does not contend that I changed my long-standing instructions or agreed to such a change. In fact, SB does not contend anything at all, since in those four months of contact they have not offered any explanation for their actions or, indeed, made any substantive response at all. SB has been thoroughly unresponsive and evasive, resisting providing me access to a complete set of my account statements ( so I could determine what happened and when, and calculate how much interest they had charged ) and, when pressed, sending almost comically irrelevant form letters that revealed a complete unwillingness to investigate the facts and discuss the substance of my complaint. As soon as I obtained a complete set of statements I calculated the total amount of disputed interest and promptly paid my entire balance less that amount ; since then, I have made timely payment for all purchases while withholding the amount of disputed interest. Although Amazon ( not SB ) has left me a series of voicemail messages confirming that, while they are investigating my complaint, I will not be obligated to pay interest, SB has added an interest charge to each monthly bill. As of today 's date ( XX/XX/XXXX ) I calculate that SB has added {$740.00} in unauthorized interest to my account ; although ASC offers a 5 % discount on Amazon purchases, the unauthorized interest far exceeds the value of that discount from XXXX to the present. As a customer, I feel that SB has wronged me, first by unilaterally and without notice or consent disregarding my long-standing instructions to fully deduct my bill each month, and then by refusing to engage with the substance of my complaint for a period which has now reached four months. As an attorney, I contend that SB has breached its contract with me, which consisted of my long-standing instructions and a consistent course of dealing implementing those instructions for a period of over four years. This breach of contract resulted in substantial potential financial benefit to SB in the form of APRs of up to 25.99 % ; it is worth noting that, since I have a high credit score, SB must have known that it ran no risk by trying to convert my 'full payment ' arrangement into something that gave SB what amounted into an option to defer collection and charge interest on the amount deferred. Naturally I have no idea whether SB singled me out for this special treatment or did the same thing to others, but I do remember that, in the not-too-distant past, SB ( formerly GE Capital ) paid a {$220.00} XXXX settlement to the CFPB in a case involving deceptive credit card practices. I have exhausted myself trying to engage SB about this matter, and I hope that the CFPB will be able to step in and force SB to undo the mess that they themselves unilaterally created.