Citibank — Credit card safety

Recently, I lost my wallet and my credit cards with it. Among the 4 cards in my wallet, only the citibank card could be misused. It was used at an ATM to withdraw cash. Without the PIN, cash was withdrawn from the ATM three times! As soon as I got the sms alert, I realised my card was missing, lodged a complaint and cancelled the card. The funny thing is, a few days before this incident, I had asked for a new PIN to be generated. This new PIN is still sitting in my house in a sealed condition. I myself do not know it, and yet the ATM transaction happened. Citibak is refusing to take responsibility in this matter.