HDFC Bank — EMI RTN Charges

I have an account with HDFC on which I took a personal loan. There was one EMI bounced in September on that loan just by 1 day for which they charged me 531(450+taxes) Rs as EMI bounce charges in September only. Now, they have deducted another 236Rs from my account as EMI RTN Charges. It is January now, why they are deducting this amount now? And they did not mention this deduction anywhere in the mail when the EMI was bounced. They did not even notify me about this deduction prior to that there will be any such deduction. How many times do I have to pay for one EMI bounce? I have been paying my every loan EMI time for so many years and this is what they are doing for one late payment for a day.