Product: Credit card or prepaid card

My name is XXXX XXXX, and this is regarding a Capital One Spark credit Card through my business, XXXX XXXX Let me start off by stating that i pay my credit card bill in full every single month, on time, using the Banks automated system for at least the last 7 years. In the month of XXXX i had a large bill of {$13000.00}. On XX/XX/XXXX I made a payment to CAPITAL ONE MOBILE PMT / ID : XXXX in the amount of {$6200.00}. I made a payment of {$6200.00} from my bank account prior to the due date. Then on the due date of XX/XX/XXXX the credit card company took the full payment that was due on auto pay on XX/XX/XXXX CAPITAL ONE CRCARDPMT / ID : XXXX in the amount of {$13000.00}. It turns out they advised me on one of my four calls to them that I should have read the auto pay details that it does not adjust the payment if you make any additional payments. So, they now have {$6200.00} over payment in their hands. 
This is where the issue has occurred. I called and requested them to put the money back into my bank account. They said they may or may not be able to but would get back to me. They did not get back to me. I called 2 weeks later to find out where my {$6200.00} was because I noticed that my credit card balance now had exceeded my maximum of {$20000.00} and they denied payment to one of my vendors. They debited my credit card account {$6200.00} which put me over my balance, but I did not get that money. I called and they told me that it takes 14 days for me to get a check back. Then they advised it is fourteen business days. Which is total XXXX, so I called fifteen business days later and I said, I do not have a check and you are debiting my account for {$6200.00} for which the bank is still holding. They advised that the check had not been cut or mailed out yet. After yelling at them I made another payment of {$2000.00} on XXXX and {$3000.00} on XX/XX/XXXX, and {$2000.00} on XX/XX/XXXX to lower my credit balance so that I would not be over my credit limit. in addition, I made my full payment that was due on XXXX on XX/XX/XXXX of {$5400.00}. However, they charged me interest for the {$6200.00}, that they said they sent to me, which they had not sent me a check. I called a third time, and they advised they would stop payment on the check, and they would apply the {$6200.00} to my account in four business days. Still no check was ever mailed to me. I still have not received any check from them, even though they say they stopped payments. How do you stop payment on a check that you have not mailed? 
Today is eight business days, and they still have not credited my account the {$6200.00}. I called today and they say it will be credited in the next two days. I do not believe them. In addition, they now have charged me {$190.00} in interest payments because they say, the {$6200.00} was not paid on my balance owed on XX/XX/XXXX, so they are charging me interest on the full balance owed. But I paid {$5000.00}, prior to the due date in additional payments. Again, I do not have the {$6200.00} in my bank account or credited to my account as of today XX/XX/XXXX. 
These are the issues the bank is in violation of : 1. They have the {$6200.00}, have not paid me any interest on my money, but have the balls to charge me interest because I carried a balance, which I believe I have not. 
2. Have held my {$6200.00} since XX/XX/XXXX and paid me no interest and have not credited my account or sent me a check. Even though each time I call they give me a different XXXX  excuse. 
3. I have called four times and spoken to several managers to get this resolved with no resolution. 
4. Have made additional payments outside my full payments upfront of {$6200.00}, as well as an additional {$7000.00} to reduce my overall balance, because if they credited my account {$6200.00} this would not be an issue. So, they have {$13000.00} of my money but continue to charge me interest. 

How is a bank allowed to do this to consumers? Even if they do credit my account, what they did should be illegal and they should be fined 1000 times the money they are holding of mine.