Complaint sub-issue: Billing dispute for services

On  XXXX , We received a call from collection agency. They claim that we owe Citibank more than  XXXX   XXXX  dollars under a Costco issued Citibank credit card. I have always set my credit card account on automatic payment option so I have no idea how and when I owe them such a big amount. The  Citibank  representative informed me an account under my name is responsible for the debt but I have never heard the last  XXXX  digits they reported to me. I dont have such a card. I then ask them to provide detailed information on whole transition history on this particular account as well as to open an identity fraud investigation.   Ever since I received the call, I have been working with Citibank representative to open a credit fraud case. This process took more than  XXXX  months and they made mistake to sent me a  XXXX  transition report, when we required the whole past history of this unknown account. Then they prematurely and abruptly closed the case, saying that I have remitted money with my other account. That is not the case. My current normally used Costco credit card were previously issued by Costco under  XXXX   XXXX . In the year  XXXX ,  XXXX   XXXX  companionship with Costco has ended so they transfer all my previous history to Citibank. Citibank then proceed to send new credit card out. They mistakenly sent  XXXX  new credit cards,  XXXX  was to my current address. Another was sent to my previous address where I have moved out   XXXX   years ago. I have changed my address and billing address as soon as I left my previous residency. So the root of my complaint is caused by this additional card they sent. The  XXXX  that was sent to my old address somehow was activated without my knowledge. And on that specific card, there are  XXXX  charges of unknown air tickets under my name. They are ordered via  XXXX , a third party travel agency website. Citibank has mistakenly link all my past transition history to  XXXX  cards then claim that I have knowledge of  XXXX , which in fact, I only know my own card. The  XXXX  cards have different account number.   With all evidence we gathered, we also opened an official identity-theft case at local police station. We have been contacting with our assigned  Citibank investigator  but she hardly ever replied. She is also quite rude and impatient when I am trying to ask for an interpreter. Citibank lowered my credit points even if I am constantly sending newly found evidences to prove my innocence. They ignored most of my calls and told me unless I help them to get back the amount that was used to buy the  XXXX  air tickets on the unknown account under my name, or find the perpetrator who steals my identity, they will not help me to restore my credit. This dispute has serious impact on my credit report of   XXXX   year.   During  XXXX  months I have made countless phone calls with Costco, Citibank,  XXXX  and police  XXXX , trying to resolve the problem that  Citibank  does n't even recognize me as a victim. They kept saying it must be me who opened that unknown account. " You just forget it '' is the typical answer I get. It is a serious insult. This dispute caused many issue to me. My son 's academic performance was also heavily impacted because he must constantly make lengthy phone calls on my behalf because I do n't speak  XXXX . Our family was deeply troubled because without my credit point restored we ca n't take any major financial decision such as moving.