Product: Credit card or prepaid card

My name is XXXX XXXX XXXX XXXX. I was an Authorized User on a Credit Card Diamond Preferred Issued by Citibank whose Primary Card holder was my sister, XXXX XXXX XXXX XXXX. 
Around Set XXXX we got a surprise when we found out that our card was frauded by someone reason why Citibank issued a new card and told us to destroy the one we had and wait while they were gon na send us a new one, which we did. The moment the new card got on the mail, we didnt even activate it and we found out that someone was taking money out of it. A total of {$1800.00} in cash advance ( $ XXXX $ XXXX $ XXXX {$300.00} ). We contacted the bank and told us to cancel it. As expected we had to dispute those {$1800.00} since we didnt use them and that balance was showing on our credit. We have been disputing this money for months until the Investigation Department of Citibank reaches out and told us that it was all good and we were not going to have to pay that money, we even got a letter saying that ( attached document ). Big was our surprise when we noticed that Citibank deposited {$1800.00} to a Checking Account # XXXX, because this account DID NOT BELONG TO ME NOR MY SISTER. Unfortunately we found out about that because our debt was not being clear from our credit. My sister has tried calling them many times for the past weeks and they deny to give her any information until she pays her debt, currently she is being harassed on a daily basis with phone calls regarding paying her debt and when she explains the situation she gets responses like we wont give you any information until you set your debt straight. 
I have personally gone to the Branch in XXXX and spoken to a representative ( XXXX XXXX ) who after digging into the system found out that apparently we were issued a care number that was already given to someone else. The Cash advance withdrawals ( {$1800.00} ) showed in this individual account but the credit showed in ours. He mentioned he never saw something like that and tried calling his supervisor who was never reachable and any other person would just tell him I dont know. Finally he filed a complaint to the Presidential Complaint on Tuesday XX/XX/XXXX and said that we would hear in 2 business days. I have personally made an effort to get in touch with Citibank through their XXXX   account, got connected with Ms XXXX from the South Dakota branch ( XXXX ) who after explaining the whole situation again told me she was gon na investigate and file a complaint to the Presidential Complaint Unit and I would hear back in 2 days. 
So far I have not heard back from any of them despite the fact that I write them but my sister keeps getting harassing phone calls saying that our due day is on the XXXX and of course if we dont pay our Credit will be affected, since now its not longer {$1800.00} but {$2000.00}. 
We have tried many times to get this problem solved but apparently the bank has no intention to hold anyone accountable for something they did and more importantly something that is causing me and my sister sleepless nights, time waste, frustration and exhaustion. 
Please I need to get this problem solved as soon as possible in an attempt not to damage my sister and my credit score since we have always been responsible when it comes to payment matters.