Product: Credit card or prepaid card

I saw suspicious charges on my Barclay's/Frontier Mastercard so paid off the balance and cancelled the card on XX/XX/2019 which was processed on XX/XX/2019 ( See  Exhibit A ) However, as I discovered today, the credit card company allowed an auto payment to XXXX XXXX be charged two days after I cancelled the card on XX/XX/2019 ( See Exhibit A ). 
I did not know that the company allowed automatic payment charges to be applied after cards are cancelled and NO notice was sent to me that a separate charge to XXXX had been made after the date of the card cancellation. So without any notice that the payment had been charged I had no idea that I owed anything. I had not used the card number to make any charges and had paid the balance in full when I cancelled the card. 
A couple of weeks later I received the new card but didn't activate it or use it therefore had no reason to believe I owed anything on the card. I did not receive a XXXX statement, possibly because we moved and have not been receiving all of our mail ) and no on-line statement was sent. So on XX/XX/XXXX when I received an email notice that my payment was late I was confused. I went on-line and found a statement without any transaction charges, only a summary of late fees, no transactions were noted. It showed a balance of {$29.00} ( See Exhibit B ) On XX/XX/2019 I wrote to Barclays/Frontier Master Card and explained that I had paid the balance in full and made no other charges. ( Exhibit C page 2 ) I asked for a phone number to speak with someone. 
On XX/XX/2019 I received a response telling me to call a number or use the on-line option looking under Activity & Statements and chose, 'Posted Transactions '. ( See Exhibit C pg.1 ) The information again verified that I owed only late fees but not what  the fees were for and that there were no purchases or transactions on the card for that month. ( Exhibit B ) I also looked at the previous statement for XXXX and found that I had paid {$1400.00} and had only had {$1100.00} in charges ... .so I should have had a credit for that month of {$230.00}, not a balance owed at all. ( See Exhibit A pg.2 )  Today, to follow up, I called the number and asked for an explanation and while speaking with the representative it was revealed to me that the charge from XXXX made after I cancelled the card was the reason. I was told that they have a right to make auto payments after a card is cancelled and that I am expected to know that even though a supplemental bill was not sent, nor was any notification sent to me that there was an additional charge after the cancellation. They didn't think it was significant that the charge was not noted on the XXXX statement as a carryover, and they themselves had trouble explaining it until they studied the billing from the previous month. 
Even knowing that it was a flaw in their own system that caused the confusion and lack of notification to me, they refused to remove the negative mark against my credit and told me I had to deal directly with the credit bureaus to see if they would do anything about it. 
Only when I insisted that they give me information on how to reach someone at Barclays/Frontier did they give me a mailing address to reach someone in their company. They refused to give me a phone number nor an email address so that I could expedite the complaint and get a resolution quickly. 
The parties that I dealt with at Barclay's/Frontier were XXXX , employee # XXXX, XXXX, employee XXXX XXXX and Operator ID # XXXX. I was told by XXXX that I could go no higher than him to find a resolution unless I wrote a letter to a second address. He also refused to give me an email address or phone number so I could correspond immediately and find a quick resolution. 
Currently I am trying to refinance my home and this negative mark on my credit may prevent me from obtaining a good interest rate of may disqualify me from getting a loan at all as it appears that I am having problems paying my bills. I ask that you help me find a quick resolution to this problem. This flaw in their system, lack of notification and lack of information has created a problem for me that will result in years of higher interest on my loan. I believe that these companies should be held accountable for informing their customers that they will continue to allow charges on closed accounts. I also believe they should be responsible for sending notices or supplemental billings to inform customers that there are new charges that need to be paid from the old billing cycle before the payments become late and incur charges and result in negative credit reports on their customers ... even though the XXXX statement did not show any new transactions and didn't note an unpaid balance or carryover from the previous statement ( as you can see in Exhibit B ) so I was kept in the dark about owing anything and thought it was some kind of mistake in there computer system. 
Lastly, I would like to receive any credit that is due to me for the overpayment I made during the month of XXXX in the approximate amount of {$230.00} as well as the fees I was charged in the amount of approximately {$29.00}. Thank you.