Product: Credit card or prepaid card

I have a Capital One credit card account. I closed that account previously with a balance I was paying off. This was my own initiative I was not forced to close the account. Recently I paid down a credit card account I have at XXXX XXXX, with a much better interest rate, and initiated a balance transfer from the Capital One Master Card account for it's remaining balance to the XXXX Visa account. I paid a 3 % balance transfer fee to XXXX and the balance transfer was initiated on XX/XX/2021. Two days later XXXX XX/XX/2021 XXXX notified me that the balance transfer was completed. At this time I begin paying interest to my XXXX Visa card balance which now has the former Capital One Master Card balance added to it. However, on the XXXX of XXXX Capital One still shows my former Master Card balance as unpaid which I will also be paying interest on ... 

Two banks claiming the same balance, both collecting interest. 

I contacted Capital One by phone on the morning of the XXXX of XX/XX/2021, after researching the transaction they insist, they have not been paid. 

I contacted XXXX explained what I had been told by Capital One regarding not being paid to clear the balance on my Capital One Master Card, and they say Capital One was paid, and I was provided with the ACH trace number XXXXXXXX for the balance transfer payment to Capital One. They said they would research the matter further, but were confident the balance transfer was completed. 

Currently two banks both are charging me interest on the same balance. I'm sure one of them is right and one is wrong. If XXXX is right, Capital One was paid, and is delaying posting the transaction and benefits by collecting interest they are not entitled to. According to Capital One published policy regarding Master Card customers, payments received are posted to customer accounts the same day. If Capital One is right, they have not been paid, and XXXX has posted a balance to my account to accrue interest that they have not actually transferred funds to acquire the balance and the right to start charging interest on that balance. 

It is my opinion that Capital One is wrong and was paid ... delaying posting payment and collecting whatever interest and fees they can, while they believe they still can. If Capital One was such a good bank, I would not have closed this account months ago, and just kept paying them off bringing our banking relationship inevitably to an end ... However, I don't know for a fact who is right or wrong, but I don't believe both banks can simultaneously own the same credit card balance and both be charging interest and fees on it. 

Attachments : 1. XXXX balance transfer history. ( indicates date balance transfer was initiated ) 2. XXXX Visa account activity. ( indicates date balance transfer posted, Capital One paid, transaction complete. I begin paying interest on the new XXXX Visa balance. ) 3. Capital One Master Card unpaid balance screenshot. ( note computer date lower right hand of screen, XX/XX/2021. ) 4. Capital One published Credit Card electronic transfer/payment policy. ( This is not the only published Capital One bank policy regarding payment posting, but they both say electronic payments received are posted the same day ... that is their policy. )