I'm sorry that you were scammed. Unfortunately, I'm certain that this was a scam.
the buyer gave the authority to deduct the money from his Citibank account in usa
The Citibank account did not belong to the scammer. The account information was phished or stolen from a real (completely innocent) person. The scammer most likely isn't in the USA. If any money was transferred into your account, it was stolen.
I mailed the bank receipt to Citibank, USA for verification.
You were never in contact with the real Citibank. The address you were given would have been fake. It is important to post this address as well, so that others will find it.
It would be very helpful to other potential victims if you posted the actual emails he sent you (delete your own personal information first) and the emails sent to you by "citibank." The scammer is likely to reuse these emails with new names and different bank accounts, so the emails themselves can be very helpful to stop people from falling for the scams and sending money to the scammers.
If you have not done so already, I would also report what happened to your police.