charged returned debit order fee

i have changed my account details for debit and was informed that it woul be debited from the new account .<br> the debit order did not take off on my old debit account and neither on the new account details given<br> i have been charged a returned debit order fee and on oth my account statements it does not show any mtn debit order taken off.the person assisting me said it was not theier fault as i changed my banking details as the magtape was already gone through but when i told her that i specifically asked if this woul affect my debit order when i was changing the banking details the person that helped me said no it will go of the new account.<br> i feel it unfare as to why i need to pay this reurned fee when i was told it would not be a problem and aslo why am i penalised when the debit order does not even reflct on my bank accounts <br>