Product: Credit card or prepaid card

CITIBANK reported an unpaid balance on one of my credit cards to the three credit Bureaus which lowered my credit scores on all 3 bureaus. The total reported balance is regarding an invalid charge which I disputed with CITIBANK.

I was charged twice for a merchandize Airline ticket after an international Airline Carrier canceled the first ticket due to a mistake from one of their agents ( Airline admitted it was a system/Agent mistake ). After this mistake, the merchant ( Airline ) charged my card again for the amount of {$2600.00} for a full fair replacement ticket. I disputed the charge with CITIBANK. However ; the merchant ( Airline ) claimed that they never charged me for a new replacement ticket. In XX/XX/2017, I received a letter from CITIBANK stating that the charge was valid and that they require further information from me to prove my claim. I provided CITIBANK with a receipt that shows the initial charge of ( {$340.00} ) on the original ticket and the new ( disputed ) charge of {$2600.00} for the replacement ticket. Additionally, I provided CITIBANK with  an internal document which I received from the CEO of the Airline that shows clear evidence that the airline agent made a mistake and the solution is to issue a free replacement ticket to the passenger. 
Unfortunately, CITIBANK failed to question the merchant ( Airline ) about the discrepancy of why I was charged twice for the same ticket. In addition, CITIBANK failed to meet the deadline to file for arbitration according to MasterCards regulations. MasterCards regulations allow the issuer bank to use message reason code XXXX which is applicable in my case. CITIBANK is refusing to provide me with any explanation to whether I proved my case or not. Instead, CITIBANKs letters stated that they are unable to help me in my dispute and that I would have to seek other means to obtain credit, or to contact the merchant directly ( which I already did ). Reality is, CITIBANK is required by law to investigate disputed charges according to Fair Credit Billing Act of 1975, and CITIBANK is obligated to file for arbitration according to MasterCards regulations but they failed to do so. 

Moreover, during my communications with CITIBANK over the phone and mail, it was made clear to me that CITIBANK has a huge failure in their system integrity. I strongly believe I lost this dispute due to mishandling and negligence on CITIBANKs side. I listed some of those points in my letters to them ( File Two pages 10-12 ) as well as a separate document ( File one pages 8-11 ). Both files are attached with this complaint.

Im attaching the following documents with this complaint : 1. Case details and timeline ( pdf file ) 2. File one ( pdf file ) which has the following : The Airline Centre internal Document, which was sent to me in email from CEO of the Airline ( This document states that the Airline agent made a mistake and as a result the Airline will issue a new replacement I '' class ticket for PAX ( passenger ) Free. ( Page 1 ) Airline response to the first chargeback claiming that they never charged me for a new replacement ticket. ( Page 2 ) The original ticket receipt for the amount of ( {$340.00} ) ( Pages 4-7 ) Indications of failure in CITIBANKs Dispute Department ( Page 8-11 ) 3. File Two ( pdf file ) which has a copies of all the exchange letters between me and CITIBANK.