Product: Credit card or prepaid card

To whome it may concern, I am a credit card customer of Citibank ( XXXX XXXX  XXXX, XXXX XXXX, SD XXXX ). I had an item advertised online for sale and somebody contacted me and offered to purchase the item by paying off my credit card bill using a XXXX account. As many people know, this is an unreliable way to accept payment and a common scam so I contacted Citibank customer service and asked them : if I receive a payment from someone online who offered to pay off my credit card bill, how long after the transfer date will the payment be truly finalized where it can not be reversed. I was told by the Citibank customer service representative that I would have to wait an entire billing cycle ( 1 month ) after the funds had arrived into the account for all payments to be settled and no more transactions will be able to be made into or out of that account. Everything will be finalized by then and all payments settled. 

So going on the advice of the CS representative I told the payer to go ahead but you will have to wait at least a month, they said ok and the {$11000.00} payment was sent on the XX/XX/XXXX, the buyer sent through all the transfer receipt details, and the payment was cleared into my account on XX/XX/2019. Then I proceeded to wait until XX/XX/XXXX before shipping the item. Immediately before I shipped out the item I contacted Citibank to ask if the status of the account or the payment had changed in any way, which they confirmed everything was in order and no changes had been made, so I sent the item out priority express as the buyer had been sending through abusive messages multiple times daily demanding that I send out the item earlier than the 1 month we had agreed upon. A few days later, on the day the package arrives, I check my credit card statement and it informs me that the {$11000.00} payment has been rescinded by the payer claiming that it was made in error. 

This was obviously a fraudulent reversal and a warning to anyone who is considering accepting payment via credit card bill pay - do not accept this method as a form of payment, the payer can reverse the transfer at anytime, including 6 months later if they choose to and even if the credit card account has been closed down. The credit card company did not contact me or consult me on the matter before sending the money back to the payer, even though I had informed them prior that the payment came from an unknown source and to contact me if anything changes with the payment. 
I contacted Citibank about this reversal and they bluntly informed me that now the money had been sent back there is nothing they can do and that I now owe them the {$11000.00} plus interest. 

I also messaged the payer about the issue but received no response, and after threatening to contact the authorities and have the item they purchased ( a watch ) registered as stolen, 1 month later I received a response from the payer saying that the reversal must have been made accidentally and that they will repay the amount that was reversed. On XX/XX/XXXX I received a payment of {$15000.00} into my credit card account originating from the same XXXX account. Then the payer demanded that I send the difference ( {$4000.00} ) to him overseas via XXXX XXXX ( which of course I will not do ) by XX/XX/XXXX or else he will reverse that payment as well. As this date has now passed the payer is now stating that they will reverse the payment immediately unless they receive the difference via XXXX XXXX.