It is not HDFC that has done the fraud, but the collection agent should have done this.
1. Did you Pay by Cheque or Cash ? If Cash you can't be careless to have lost the receipt.
2. It is il-legal to call somebody for extracting money. Lodge a Police complaint against them and also file a complaint with RBI.
Indian System is Built on a Solid Layer of Corruption, don't be WEAK, BE STRONG and Fight Them. By Crying you will reach no where. Face them Boldly.