There was a previous post on this, and I wanted to reply, but was not able to do so.
So here is my response:
A couple of months ago, I had the same problem with my Citi Double Cash, although wife's Citi Costco worked fine. Everytime I tried to log in, it would ask me numerous security questions. I answered correctly, but it would tell me the answer was wrong and block me out( I mean, I think I know the city where I was born and my own birthdate).
No matter what I did, it kept blocking me out. CSRs knew nothing, as usual.
Finally, out of desperation, I downloaded Citi mobile to my phone, with a different password, and it worked fine. However, man does not live by phone alone, and I grew frustrated not being able to get it on the computer.
I was at the point where I was going to sockdrawer the card and just convert my Chase Freedom to Unlimited and use that.
Then, miraculously, I must have reached the point where they ( the credit card Gods at Citi?) finally decided that I was who I said I was, and it started working.
However, as blissful as things are 
, I will not put up with this again, not even for 2%. Next time this happens, I WILL convert Freedom to Freedom Unlimited and take the 1.5% for everyday spending. Citi is way too high maintenance, and life is too short (at my age) to worry about the extra half percent. It won't change my lifestyle !!
I too was having problems on Citi's website until last week when it seemed to work just fine. I am not very impressed with Citi's IT department. Citi's website is not the most user-friendly that I have come to expect from a prime lender.
I’ve had the same issues with my Citi DC. It’s my least favorite card. I’m not about that high maintenance life.
