Product: Credit card or prepaid card

I used two balance transfer promotional offers from Bank of America, one that expired onXX/XX/XXXXand the other active until XX/XX/XXXX. On the first offer, I was charged an interest of {$60.00} on a remaining balance of {$3500.00} on my XX/XX/XXXX -XX/XX/XXXX statement ( APR = 20.74 % therefore, interest = 20.74/XXXX*30/365* {$3500.00} = {$60.00} ). I then made a payment of {$3600.00} onXX/XX/XXXX. Any payment in excess of the minimum monthly payment is supposed to go to the account with higher APR first. My total balance at this time was {$6900.00} and the minimum payment required was {$120.00}. I also made a purchase of {$240.00} in this billing cycle ( purchase APR = 17.74 % ). I was expecting the balance on my first balance transfer to be lowered by around $ 3600.00- {$120.00} = {$3400.00} which will make it $ XXXX- {$3400.00} = {$63.00} or somewhere around that going forward. However, my XX/XX/XXXX -XX/XX/XXXXstatement shows this balance to be {$2300.00} and I was charged interest of {$41.00} on that ( 20.74/XXXX*31/365* {$2300.00} ). I believed this was an error and hoping that it will be rectified, I called the bank onXX/XX/XXXX. After longer than an hour on the phone and transferring between three customer service agents, all I got was that they basically admit that it is a mistake but were unable to correct it. One agent even mentioned the {$2300.00} is not a real balance, but it is a projection. However, the interest it accrued is added to my total balance of {$3600.00} ( {$6900.00} - {$3600.00} + {$240.00} + {$41.00} + {$1.00} ). You can also see that it is a bogus number because my total balance currently is {$3600.00} but the balances on the two balance transfer offers are written on my latest statement as {$2300.00} and {$3300.00}, which wo n't add up. The final agent mentioned the previous agent has tried to initiate a refund and she was not successful. Then he told me that I would get a detailed explanation of how I got charged the interest through mail with options to go forward. Today I received a letter datedXX/XX/XXXXfrom Bank of America and to my surprise, the letter stops mid sentence trying to explain the reason I was charged interest. This is appalling and it looked borderline fraudulent in all honesty. To make sure that the letter is indeed as it was, I called the bank again today and the first agent confirmed that it is sent from them. She in fact tried to tell me the reason I was charged interest and stopped midway. She said she was attempting to read me from the letter! Then she transferred me to another agent ( named XXXX ) and it was the same thing all over again. I asked the amount I needed to pay on the next payment date ( which is XX/XX/XXXX ) to avoid paying interest and the amounts I was told range from {$55.00} to {$3300.00} plus. All did n't make sense though because of the bogus calculation on my current statement that I explained above. I asked for an email address to address my concern further up but was told that I had to do that from my account but the online support is no longer available from there. And there is no way of contacting the bank by email in this day and age! Then I requested the agent to file a complaint/claim on my behalf or escalate my case to her superiors. After trying for a while, I was told that that was impossible too. I then indicated my intention to file a complaint but other than asking for apology, there is nothing that the agent was able to do to solve the issue. I am afraid that the bank will continue to charge me interest on non-existent balance whatever amount I pay next. Therefore, I am forced to file this complaint with the hope that I get a fair resolution. Please refer to my bank statements that I referred above and the letter I received today. Comparing the two statements clearly shows the glaring mistake that I tried my best to explain above.