Forcing to credit extra amount for loan

Location/place: Hyderabad

Name of company/service: HDFC,Hyderabad

I have took a personal loan in Dec,2009 of 1.28Lakhs for 36 months(Rs.4692/- EMI).I am regularly crediting the loan amount (Rs.4692/- EMI)on 3rd of every month,as 4th is my due date.Till 2 1/2 years I didn’t receive any calls but from couple of months,i am receiving the calls to credit extra amount.When question for that,there is a mismatch in the hierarchy replies.I am only maintaining the account for crediting loan amount,not doing transactions or using any services.Still their claim that due some cheque bounce’s (in Oct and Nov 2010)there are reducing the amount.In Oct,Nov’2010 they have already reduced the due amount along with the loan amount.Here I could see,they need a reason for reducing the amount.When I asked for the close amount(for 5months),they reported Rs.25,800/-.I couldn’t get that.Please kindly help me.