Product: Credit card or prepaid card

I use my Synchrony Bank Amazon store card to make purchases with a " no-interest '' promotion. I must pay the full balance of a particular promotional purchase within 6 or 12 months, depending on the purchase amount. Some purchase balances must be paid before others, so as to avoid paying interest at 25.99 % ( APR ). Of the promotional balances on my account, two are expiring this month ( XX/XX/XXXX ). The total amount remaining to pay off these balances is {$360.00}. If that total is not paid this month, I will be charged {$290.00} in deferred interest that has accrued over the past 12 months. At the start of this year, I calculated the amount I would need to pay each month in order to pay off these balances on time. By scheduling a monthly autopayment of {$340.00}, the balances that are coming due this month would be paid off in full. I assumed that Synchrony would apply each payment to the earliest expiring balance. 

When I received my XXXX statement, I realized Synchrony had applied small dollar amounts from my $ XXXX/month payments to all promotional balances, including balances expiring later this year and in XXXX. On XXXX, I called Synchrony bank. All customer service representatives I've spoken with about this have been courteous, patient, and understanding. One rep explained that Synchrony " must '' apply these " nominal amounts '' to all balances. She stated only after the first {$29.00} ( minimum payment amount ) of each month 's payment has been split between all balances will the rest of that month 's payment be applied to the earliest expiring balances. This seems to be consistent with the cardholder agreement, and I have a better understanding of it after reviewing my statements again. Because {$29.00} of each {$340.00} autopayment had been applied across all balances, the XXXX autopaymentfalls {$27.00} short of paying off the expiring balances. I discussed this with the Synchrony representative. I made a manual {$100.00} payment, while on the call, to make sure the expiring balances were paid. The rep assured me it would be applied only to the promotional balances expiring in XXXX. The rep did not tell me that Synchrony would then automatically reduce my scheduled autopaymentamount by {$100.00}, defeating the purpose of making an additional payment and still leaving me {$27.00} short. Synchrony'sonline payment page also does not tell users this, nor does their cardholder agreement. Synchrony sent a letter to specifically tell me the {$100.00} manual payment had been applied to the promotional balances I requested, but it did not mention they would just reduce my autopaymentamount without notice. Had I not checked my store card account this week, I would be out {$290.00} in just interest. 

Before modifying my scheduled payments, which Synchrony promises to draft and process on time each month, I need to be notified. Ideally, reps or the online payment page would have explained it at the time I made the manual payment. Instead, Synchrony'ssystem sets users up to fail to timely repay promotional balances. Today, I called Synchrony again to ask why I was not notified. After being placed on hold by representative for 45 minutes, the call was disconnected.