Citibank — Unauthorized credit charges debated for months

In August 2016 we were on a world tour visiting family in UK, Cyprus, N.Y and Canada, making stopovers in Singapore, Zurich and Vienna.
Our citi credit card did not work for us on presentation on 17th August. We used a different card. 10 days later in Amsterdam our card was rejected again. I found that our card had been hacked and maxed out.
Not only that, but I have never used the secondary card (in a protective case in my possession).
After months of harrassement and stress we cancelled the secondary card was never renewed and we cancelled our relationship with Citi in January, 2017 after paying everything we truly owed.
Now, 7 months later I received a letter with tiny pictures of strange people's passports (5 different faces and birthdates and genders). I am being asked to give another account and if not my card will be debited again. There is one day remaining on the time frame to respond.
We sent our passports and itinerary to Citi and statements about everything and still they cannot understand that these people are criminals who have used our cards for a fraudulent transaction. I am white, Irish. These are black and Asian in name and complexion. Why am I being harrassed at 68, with cataracts' operations due in a few weeks, reading tiny writing in foreign languages from a place we never ever visited in our entire lives, let alone in 2016. Such harrassement and senior abuse is appalling. Can I get them to stop sending these fraudulent and nasty letters that put me under time-stress and try to turn me into a criminal and not a victim of fraud. Citi knew about these transactions in August and sent text messages but we had already left and were using a different international sim. When will there be justice and a little compassion for ordinary victims of crime?