Product: Credit card

Synchrony Bank underwrites my Rooms to Go credit card. I am participating in a 0 % interest promotion for 60 months. In order to qualify for such a promotion, a customer must have a good to excellent credit history. I work very hard to ensure that all of my debts are paid before their listed due dates. 
In XXXX 2016, Synchrony charged me a late fee stating that my payment was not processed by my statement 's due date. In XXXX 2016, I was charged another late fee in a higher amount because I did not pay the minimum payment on my XXXX 2016 statement. I received XXXX emails, that went to my junk folder, and XXXX mailed communication stating that no payment had been received, which was false. My issue is, on the statement Synchrony states, " Payment due by XXXX XXXX on the due date. '' My due date for my Rooms to Go credit card is the XXXX of the month. I have an electronic payment sent from my financial institution automatically each month on the XXXX. If the XXXX falls on a Saturday or Sunday, my bank will send the payment out on the Friday before the XXXX. When I spoke to individuals at Synchrony, they stated that it takes 3-5 business days to process payments. In their words, I must ensure that my payment is received by Synchrony five days before the due date listed on my monthly statement. When I asked to find out when my payments have been received by Synchrony, I was informed that I would need a subpoena to obtain that information. I was also informed that it did not matter if I sent a personal check, a check from my bank account, or an electronic payment as they all take the same amount of time to process. 
Synchrony is sending out monthly statements that state customers have a specific due date, yet they are enforcing an unpublished policy that all payments must be processed before the stated due date. Because of their unpublished policy, they are assessing late charges and interest and jeopardizing consumers participating in zero interest promotions, which could potentially damage our creditworthiness. As part of our credit card agreement, we must make our payments on time or risk losing our promotional APR and paying an astronomical 29.99 % on large-ticket items. 
There is a big difference between receiving a payment and processing a payment. A company can hold on to a payment for as long as they want to before they process it and a consumer has little to no recourse. Surprisingly, when I demanded that the late fees and interest be removed from my statements, Synchrony did this with little to no fanfare. When I asked for documentation of the outcome of our conversation, they refused stating that confirmation would be listed on my next statement. I demanded documentation again and was told it would take 24-48 for them to send me an email. It has been over 48 hours and I am still waiting. 
As a side note, my husband is the primary account holder on a BP credit card also financed by Synchrony. For that card in XXXX they charged interest and a late fee stating that payment was not received by the due date. Again, this was a situation when Synchrony had received payment before the due date but did not process the payment for several days. 
I now live in fear that Synchrony will enact some other unpublished policy that will adversely impact me and force me to pay an astronomical interest rate on my furniture purchase.