Citibank Credit Card
Wrongly debiting charges

I have a citibank gold credi card and they have started debiting interest charges on a magic calculation every month. When i asked for clarification over the telephone helpline number, they told they will call me back with the details, nothing happend.

now they are telling they will forward the information to Credit information beauro of India and they will list my profile negative. I told them very clearly, they will have to pay for that too if they does it.