Complaint sub-issue: You never received your bill or did not know a payment was due

Due to job related XXXX and derivative conditions, my XXXX made me fly to Washington, D.C. to interview prior to taking away my security clearance, and removing me from service on XX/XX/XXXX. I asked the interviewing employees how was the trip going to be paid for. The agency stated they would pay for all expenses involved and pay off the XXXX travel card, which they confiscated from me. I was not allowed to clean out my desk once I returned to pick up my stuff. Someone else did that and met me at the main entrance to the office building I worked in. The XXXX has sent me NO bills for the credit card to this date XX/XX/XXXX. On XX/XX/XXXX, I received a notice at my home address from an entity with a P.O.Box claiming they were from Citibank, that stated that {$610.00} was past due on a 'Citi XXXX   Card ' in my name, and that a delinquency had already been reported on my personal credit report. I never received any bill prior to that as they would have been sent to the my agency, was unaware of any expected bills, and was given no notice of reimbursement to pay any bills by my former XXXX. I called the so called Citibank, and they said they would harm my credit more, if I didnt pay immediately. I advised I had no notice, nor information that what they were sending me was correct. They said I had to pay immediately or they would harm my credit. The fact I had never received a bill prior to their threatening letter, had never been advised by my prior agency of any bills due, and the illogically high pressure they tried to apply to me to pay them, clearly indicated to me that this was a scam. My former XXXX  is notified every time a travel card is 30 days, 60 days, etc late, at the executive level, logic would dictate they would have contacted me. My entire agency 's information was leaked and posted to the internet several years before, including contact info, so fraud would be very easy to commit in this situation. I left a message with the agency 's Finance office, however COVID protocols were now in place and I never received a reply. I did not hear anything else about this from either the XXXX, or the people claiming to be Citibank. Again, a sign that this was a scam. I paid my house off in early XX/XX/XXXX, so I checked my credit report on XX/XX/XXXX expecting it to be maxed out, and I was startled to find that my credit score had fallen from over 830 to XXXX because of this {$610.00} bill that I was never billed for. Keep in mind, again, I had NO ABILITY to access anything sent to my XXXX  office, and my card should have been closed in XX/XX/XXXX, not when I received this threat in the mail stating it was closed in XX/XX/XXXX. Ive worked very hard to get my life back together after going through horrible events that most could never imagine. My reward for service was this con job. Im in the process of purchasing and building businesses. These people made no attempt to appear legitimate and they were very rude on the phone. If I had any evidence they were legitimate, I would have paid this cheap bill the moment I was billed. Ive disputed the debt to the credit bureaus. Additionally, the agency had changed travel card companies within a year of my departure, I had other XXXX  credit cards for multiple other purposes, I don't even know that they used Citibank. I still believe this is a scam.