Hero Fincorp — I paid my emi on before the due date online but they making cheque bounce charge

My application I'd no 7442174(r.kala).I paying my dues online regularly in past 8 months due to avoid unwanted charges deducted by your side and bank side. I clearly maintain the required amount for the loan in bank account but at the particular day they charged something else charge so the payment was unsuccessful on that day.. So I raised a issue and requested to them I'll pay regularly online before the day. But now only I noticed that I paid my due before one day but they charge the bouncing charges for that. What is this? I spoked to your service they said I'll clear the overdue amount kindly pay this month emi.. But till now they didn't clearit . Kindly work on it otherwise I'll didn't pay further emi and raise a complaint in the legal side.