I thinks my credit card due date at 31st. But I have pay the credit Bill at 2nd of the months. They have charges me more than 100 Rs. I cant understand the payment for credit and how to use it.

You need to ensure that you pay before (and try to make it about a week before, in case of any issues) the due date. So instead of setting up your direct debit for 2nd of the month set it up for the 21st or something, ensuring you have paid the previous month and are up to date with payments.

In my point of view setting up direct debut is not recommended at all because it is similar to giving your controls to banks. I know most of the people here may not agree with me but once a wrong amount is deducted from your own account then its you who has to run around collecting statements and all that what you are not interested in doing. Better is to either pay via cash or cheque, rest is up to you.