Standard Chartered Bank — late payment charges on credit card

I am a student and pursuing my higher studies in united states. Prior to this i was employed in a company in india. Few days back i made a payment from and as i was traveling could not make the payment on time (Late by 3 days only). For a transaction of 800 they have charged me 620rs late fee.
Before coming over here i was being assured by the bank representatives that i will be getting full support from bank regarding my international and domestic accounts. But now not only denying any help also mentally harassing by keeping me hold for long time and disconnecting the call in between.