Complaint sub-issue: Can't use card to make purchases

I have been a Citibank customer and a user of their Citi Cards AAdvantage program in good standing for a number of years. However, this relationship has soured recently becoming the source of an excruciating frustration for reasons totally unknown to me. 
The current situation began during the second week of XX/XX/2018 when I moved from XXXX  to XXXX. Before departing XXXX  I visited my ( to this date ) Citibank branch and placed a change of address.Shortly after moving I received from Citibank in XXXX XXXX, XXXX  a " Confirmation of Account Change ( s ) '' dated XX/XX/2018 showing my previous and current addresses. This letter was mailed to my XXXX  address.and forwarded to my XXXX  address by the Post Office. I  received an identical letter that was mailed directly to my current address. Shortly after I received from Citi AAdvantage in XXXX XXXX, XXXX a " Request to confirm account activity '' dated XX/XX/2018. Among other statements the letter indicated " We are concerned about potentially suspicious activity on your Citi/AAdvantage Gold World MasterCard account. : The letter includes other statements such as a phone number to call their office " right away, '' and " Until we hear from you, merchants may ask to verify your identity before they approve a transaction using your card. '' I immediately called the number provided and since then I have made a number of calls to the financial institution at different days and times to numbers they provided to me, each call always causing me to go through the same unending questionnaire and no answers to my questions as to what is the problem, what is causing it to not be resolved, and what if anything can be done to resolve it. 
On one occassion I was told to expect a call from their office WITHIN THE NEXT HOUR. At the end of another frustrating telephone call I was told to expect a telephone call from their office IN A FEW SECONDS. I have never received any such all or any call from Citibank and/or Citi Cards In fact to this date I have NOT received from the financial institutions named above any information at all as to what is the problem. In addition to the telephone calls that never arrived, several weeks ago during one of my many calls, I was told to expect a letter to which I was supposed to respond. No such letter has reached my home. I must note that any time i try to review online any of my Citibank accounts I am first advised on the computer : " We apologize for any inconvenience, but to protect your account further charges may be limited until you have contacted our customer service department. '' Recently, on XXXX XXXX I made one more attempt at finding what is going on and how to reolve it. Once again I was put though the same questions I have been asked an incredible number of times, placed on hold, receiving no answers to my questions and finally being told to expect the previously mentioned telephone call I was to receive in a few seconds. After waiting for much more than a few seconds and having received any calls, I placed a call and requested to talk to a supervisor. A Miss XXXX identified herself as a supervisor, once again I was asked the same questions I had answer before and I even attempted to provide Miss XXXX with additional information I thought would help in determining my identity, all to no avail. When I complained to Miss XXXX about the discrepancy between the many instructions to call the customer service department only to be put time and time again through the same interrogatory without receiving any information I was asking for and the misleading information I was given about expecting telephone calls and mysterious letters neither of which have I ever received, Miss XXXX asked for my telephone number which I gave to her only to be told that phone number was not useful to her to obtain whichever ( secret to me ) information she needed. She then asked if I have another telephone number I could giver, to which I agreed by giving her a cell phone number which as the land number I gave her a few minutes earlier was not useful to her. Since then I have been wondering what type of telephone did Miss XXXX expect me to have that would satisfy her needs. I must add that the conversation came to a conclusion after Miss XXXX brought up the issue of a letter I was going to receive from her office sometime between the next five to ten days. I asked Miss XXXX if she could mail me the letter via express mail or overnight as I need to have this situation resolved asap, she indicated to me that she was not authorized to mail anything other than via the regular mail. To this moment I have received any mail regarding the pending issue ( s ). 
I want to apologized for the length of this complaint but I did not know how to describe this incredible frustrating situation. I am a XXXX years old man hoping to enjoy whatever time I have left on this good earth rather  than spending it making telephone calls, writing complaint letters or dealing with insensitive people apparently unqualified to deal with the attention and care a good customer in any business deserves. 
My concerns : I have had an excellent credit rating for some time which I am afraid it might be declining due to this frustrating situation. 
I am concerned over the fact that throughout this situation I have been unable to obtain any information regarding what is the problem, the reason for it to occur, and/or how to solve it. And finally I was recently publicly embarrassed on two occasions, once when I was attempting to make a purchase at a local well-known store and again when I invited friends out to dinner only to be told that the credit card I was trying to use was not acceptable. 
Your help in getting an explanation of the problem and a solution to it will be greatly appreciated/