Update
Have received a letter from Citi over the weekend. Essentially it is the SAME letter together with the Declaration of Unauthorized Use Form that an earlier email instructed me to download both from the Document Center at Account Online. However, the attached blank Declaration Form has a slightly different reference number at the bottom under the bar code when comparing to the downloaded one.
I dont think I need to fill out this newly arrived blank form again. Just to be on the safe side I called Citi dispute dept to inquire if I still need to fill out this form. The CSR put me on hold and then came back to tell me only Security Dept can answer it and she transferred me to Security Dept.
A very helpful woman based at South Dakota told me they got the previously sent in form and the case was now considered closed. I asked that since the description shown under the reversals is "Security credit - Item under Investigation", would I receive a written communication from Citi to inform me the Investigation is completed and the Credit is Final? She said No, there would not be a written communication. As far as she can tell from the system, the case is closed. But if I like to receive a confirmation letter, she can inform Customer Service to send me one to that effect. (Yes, I do want to have a confirmation letter though I am not sure if I ever will get one!)
There is yet another 800 number if one needs to contact Security Dept - that is 1-800-950-5114, given by this CSR.