Citibank Credit Card — Reducing the credit limit drastically without prior notice

I have been using citibank credit card for the past 4 years. The credit limit of almost 1.1LAKHS was all of a sudden reduced to 10000, without any prior notice. I was surprised when the card was declined at a PoS. All these had happened inspite of paying off the total amount due/ much more than minimum amount due amount every month. On contacting the customer care, the citiphone officer was neither pleasant enough in explaining the reason nor was ready to register this as a complaint...
its really frustrating...and have just cancelled the card..