Complaint sub-issue: Credit card company isn't resolving a dispute about a purchase on your statement

On XX/XX/XXXX XXXX XXXX came to my home to demonstrate a vacuum cleaner which I subsequently agreed to purchase for {$1800.00}. At that time, Mr. XXXX took my credit card number and processed the transaction for that amount ( as is noted by the paid in full on the receipt. ) When I received my Estatement in XXXX from Citibank, I was fully expecting the {$1800.00} charge to be included as I had, indeed, authorized a single transaction for that amount in XXXX. I subsequently paid the bill. 
In my XXXX Estatement, I noticed that the amount was particularly high so I reviewed the statement and saw that Mr. XXXX had charged me for a second time on the single purchase that I had made in XXXX. I attempted to call Mr. XXXX multiple times but he would not answer his phone. I was able to finally get in touch with him through a lengthy text conversation. During this conversation, Mr. XXXX stated that I should simply call the credit card company to have this issue resolved. I immediately called Citibank and informed them that this was a fraudulent charge. They issued me temporary charge back and said they would investigate. They subsequently asked me for more information which I supplied. Included in that information was a copy of the original sales receipt dated XX/XX/XXXX, and a copy of the screen shots of the text conversation I had with Mr. XXXX in which he states that the credit card company will get the money from from the terminal.its called a vendor chargeback. 
I have spent the last 8 months calling Citibank about this charge while they transferred it back and forth to various departments. I have provided them with ample information showing that I only authorized ONE SINGLE transaction, not two. I spoke with a Citibank employee who told me this was a fraudulent charge so the matter was sent to the fraud division. Citibank closed the initial credit card account and opened a new account under my name ( which I did not request ). Since then I have been unable to access information for the original account, including payments, transactions. etc. 
On XX/XX/XXXX I received a letter stating that the fraud department had closed their investigation. I was confused by this as I had just spoken with a supervisor the day before regarding my case and she ( her name was XXXX ) told me that Citibank was looking into the matter and that someone would be contacting me within 10 business days. 
On XX/XX/XXXX, I received an email from Citibank titled Update on your dispute. I attempted to open up this communication to see what was happening with this case but every time I have attempted to do so, I get an error message saying that the online account information is temporarily unavailable. Yesterday, XX/XX/XXXX, I attempted to login again and I still receive the message Were very sorry. AccountOnline is temporarily unavailable. 10 days later and it is still inaccessible, so I called Citibank to check on the progress. They told me that they were not going to reverse the charge and have subsequently charged me interest on the disputed amount. I have exhausted every means I have to resolve this matter including filing complaints with the XXXX XXXX XXXX and The State Attorney Generals Office, but to no avail, so I turn to you for assistance with this matter. I am unable to provide you copies of communications with Citibank as their online system has been down for at least 10 days now so I am unable to access those communications. I will gladly forward them to you as soon as their system is working.