Citibank Credit Card Complaint

Citibank Credit card department,

Closing/Cancelling account Florida

I closed my - last -/-/- and also closed my Costco account. I got a credit from Costco on -/-/2016 for $55.00 on the - that I then closed. Costco changed credit card companies months later and I got a new Citi ( Costco ) card that I did not want or order. I never activated it. Now almost a year later I am getting late notices from Citi that I have not paid my bill and they have added $25.00 in late fees. I called them last month and told them I never opened a card and they said that they would close it. So now today I get another bill from Citi that I am - past due. This is fraudulent since I never opened the card and at the time of their transition, I was not a customer of - or Costco. I have great credit and now it will be wrecked over this fraudulent charge. I am getting no where with Citi.