[Resolved]  Citibank Credit Card — Interest rate is calculated for paid amount also

Address:

Tiruvallur, Tamil Nadu

I got a bill amount for Rs.28820/- and paid Rs.28000 much earlier than the payment date.
This month i got a bill with interest calculated for nearly Rs.1200 (service tax+interest) for the unpaid amount 820.
They have calculated more than 100% interest rate and convincing me that i have made a part payment (Rs.28000 is part payment!!!!!!!!) and hence the interest 1200...and telling this is the policy of their credit card company. Its mentioned in terms and conditions...

I want to SUE this company for this malpractice.

Kindly someone help me how to file a case against them...