Product: Credit card or prepaid card

I was recently reviewing statements for my XXXX XXXX credit card that I have through Chase and identified a concerning trend in which they have been overcharging me interest on purchases made on my credit card in the months following promotional balance transfers. Here is a timeline and explanation of what has occurred : I made promotional balance transfers in XX/XX/XXXX and XX/XX/XXXX for {$8000.00} and {$15000.00}, respectively. There were {$400.00} and {$600.00} fees associated with those transfers. Subsequent to those transfers, in the months between XX/XX/XXXX and XX/XX/XXXX, I have been charged interest on balances that do not appear to correspond to the actual purchases I have made that are not subject to the promotional interest rates. As an example, in XX/XX/XXXX I paid off my previous balance in full and incurred new charges of {$570.00} and fees of {$400.00} ( associated with the promotional balance transfer of {$8000.00} ). This corresponded to a new balance of {$8900.00}, of which {$970.00} would have been subject to interest in XX/XX/XXXX if not paid off before the statement closing date. In XXXX, I made purchases of {$2400.00} and had statement credits and made payments totaling {$500.00} before the close of the statement. The {$2400.00} purchases should not have been due until the close date for the next statement. Therefore, only {$470.00} in purchases should have been subject to interest in XX/XX/XXXX. However, Chase reported {$1700.00} as subject to interest for the next statement. In that month, it seems that Chase either charged me interest on : ( 1 ) a balance that I had already paid off, ( 2 ) a balance that was not actually due yet, ( 3 ) a promotional balance that should have had 0 % interest until XX/XX/XXXX, or ( XXXX ) a made up balance. 

This same issue has happened in nearly every month between XX/XX/XXXX and XX/XX/XXXX with an average of {$1500.00} excess balance that I was charged interest on. Furthermore, in XX/XX/XXXX, I attempted to pay off most the entire balance that Chase reported as subject to interest in my previous statement ( {$2500.00} ; reported in the XX/XX/XXXX statement ), as well as all purchases that I had made in XXXX ( {$1700.00} ), for a total payments and credits of {$4100.00}. This value was only ~ {$250.00} less than those combined balances. In the next statement, I was still charged interest on {$2100.00}. I can think of no conceivable explanation based on the information that Chase provides me in my statements other than that they have been charging me interest on promotional balances that should not be accruing interest. Additionally, Chase 's credit card statements appear to be purposefully designed for maximum confusion. I still have not figured out how to determine the amount of money that would be subject to interest in a subsequent statement period using the statements provided to me by Chase. My earnest attempt in XX/XX/XXXX to avoid getting charged interest was completely unsuccessful. 

I will attach my credit card statements from Chase for the period of time discussed above, as well as a summary table that shows the previous balances, payments and credits, purchases, balance transfers, interest assessed, fees, and new balances from each month ( XXXX XXXX XX/XX/XXXX ). I have included in the table the balance that Chase reported as being subject to the standard interest rate for purchases. Based on the values in my statements, I've tried to calculate the actual balances that should have been subject to interest based on the purchases and payments made in each statement. I've also calculated the interest I should have been charged based on those calculated balances and the amount that Chase overcharged me. For example, in XX/XX/XXXX, I calculated the amount of interest that should have been charged on the {$470.00} balance at {$8.00} ( in the column titled " XXXX XXXX '' ) and the overcharged interest at {$22.00}. In subsequent months, I've subtracted the overcharge from the previous month from the actual balance ( see column " Actual Balance Minus Interest Overcharge '' ) to try to account for the additional compounding from overcharged interest over time. 

Between XX/XX/XXXX and XX/XX/XXXX, I have calculated that Chase overcharged me a total of approximately {$460.00} in interest. I am deeply disturbed that this would happen and was not caught by anyone at Chase working on my account. I contacted Chase on XX/XX/XXXX to try to resolve this issue or have them explain to me how I was incorrect in my calculations. I requested that the provide me with documentation showing how and why the balances subject to interest were assessed. They responded later in the day on XX/XX/XXXX with a relatively generic message that neither addressed my questions nor provided me with any information that I could use to understand or resolve the issue I encountered. They offered to provide me with the terms of the promotional balance transfers, but I did not take them up on that offer. These documents are long confusing diatribes full of legalese and jargon that seem to be specifically designed to confuse customers so that they will inadvertently incur unnecessary fees and interest when merely trying to optimize their finances. Based on the unhelpful initial response from Chase, I am doubtful that any further correspondence with them from me on my own would yield an appropriate response.