During my XXXX billoing cycle, BofA charged me {$30.00} in interest, even though I paid the previous month 's balance in full, as shown on the XXXX billing statement ( attachment ). This is my first inquiry. 

Also during my XXXX billing cycle, Bank of America issued me a credit of {$10.00} for a fee they waived from my account. Therefore, at the end of the billing cycle in XXXX, I paid my full balance minus {$10.00}, assuming that the {$10.00} refund would apply towards my account balance. 
However, in the XXXX statement, I was assessed an interest charge of {$31.00}. When I called Bank of America to ask why, they said that I had underpaid by {$10.00} because the {$10.00} refund of the fee did not apply until the next billing cycle XXXX. My second inquiry is this : if the {$10.00} appeared on the XXXX statement as a credit, how can they not apply it toward my outstanding balance? I believe this is deceptive. 

I then asked how a {$10.00} underpayment could lead to {$31.00} in interest. They told me that underpayment on the account causes any purchases after the underpayment to be considered part of the average daily balance, even if they are part of the current billing cycle which is normally subject to the usual grace period for payment. This is the third inquiry. This explanation does not make sense to me, nor can I find it documented in the Terms and Conditions of the card. Extended questioning of over XXXX minutes with the customer service representative also did not yield any clear answers - they just kept referring me back to the Terms and Conditions. 
