Product: Credit card

I have a promotional balance on my credit card with a 0 % interest rate that stemmed from a promotional check written XX/XX/XXXX. On XX/XX/XXXX I made a purchase for {$340.00} and on XX/XX/XXXX for {$6.00}. On XX/XX/XXXX I made a payment of {$650.00}, which is well over my purchase amount and minimum payment of {$69.00}. 
XX/XX/XXXX statement closedXX/XX/XXXX {$4.00} interest chargedAccording to them they charge interest from the day the transaction posts until it is paid off. Also according to them, minimum payments are applied first to the lowest interest balance ( in my case 0 % ) and then any payment amount over the minimum is applied to the highest interest balance ( my purchase balance ). They state payments are posted the day they are received. After my above payment, my opening daily balance subject to interest on XX/XX/XXXX should have been XXXX. I have had issues since. I have made numerous calls, gone to numerous branches, and sent numerous emails. I have requested a list of my daily balances like all my other credit card companies provide. This was their response : '' At this time, we can provide you the formula used to calculate interest and a copy of your billing statements showing the outcome. We do not have specific criteria with numerical data as this is an automated billing process. As required though, in your monthly billing statement, we do specify your balance subject to interest, the corresponding Annual Percentage Rate ( APR ) and the amount of interest charges billed to the account. " XXXX From Chase : '' To calculate your balance subject to the interest rate, we start with any balance carried over from the previousday and add new charges or fees then SUBTRACT NEW PAYMENTSor credits. This gives us the daily balance for one day. " " Next, we add together the daily balances for all days inthe billing period and divide this total by the number ofdays in the period. This gives the balance subject to theinterest rate for the billing period. " Adding together my daily balances = {$8100.00} / 31 days in billing period = {$260.00} ( bal sub to interest rate ) 1. 15.24 ( interest rate ) / XXXX = XXXX. XXXX x XXXX = XXXX. XXXX x {$260.00} = XXXX. XXXX / XXXX = {$3.00} interest for that statement. ( I was charged {$4.00} ) Statement XX/XX/XXXX to XX/XX/XXXX : Daily purchase balance subject to interest rate is XXXXfor all days not listed, since all purchases should havebeen paid off as outlined above. 
XX/XX/XXXX XXXX ( purchase XXXX + purchase XXXX ) XXXX XXXX XXXX XXXX XXXX ( CASH PAYMENT IN BRANCH {$2400.00} ) XX/XX/XXXX XXXX ( bal subject to interest rate ) XXXX XXXX ( purchase ) XXXX XXXX XXXX XXXX XXXX ( payment posted {$700.00} ) I already paid myminimum payment so this entire payment should have gone tothe purchase balance of {$450.00} on XX/XX/XXXX, the remaindertowards the 0 % balance ) Interest for that statement:XX/XX/XXXX-XX/XX/XXXX daily bal was XXXX x 4 days = XXXXXX/XX/XXXX-XX/XX/XXXX daily bal was XXXX x 4 days = XXXX + XXXX = XXXX / 30 days in billing cycle = {$190.00} bal subject to interest1. 15.24 interest rate / XXXX = XXXX. XXXX x 30 days in billing cycle = XXXX. XXXX x {$190.00} = {$240.00}. {$240.00} / XXXX = {$2.00} interest for that statement. Iwas charged {$10.00}. 

Statement XX/XX/XXXX to XX/XX/XXXX : The only transaction the whole cycle was a payment on XX/XX/XXXX for {$510.00}. ( I was charged {$19.00} interest for this period in which I had NO PURCHASES meaning XXXX DAILY BALANCE. This is when I was told I was charged interest because of double billing cycles. ) Statement from XX/XX/XXXX to XX/XX/XXXX : I was charged {$12.00} in interest, no purchases for two cycles.XX/XX/XXXX payment of XXXX. 
Statement from XX/XX/XXXX to XX/XX/XXXX : Charged {$5.00} in interest, no purchases for three cycles now. XX/XX/XXXX payment of XXXXAccording to their stated formula, they have been applying my payments wrong and refusing to fix it.