HDFC
Charging more on credit card

Dear Sir,

I am a customer of HDFC bank.

Problem: I have gold master card.. I had purchased worth rs 900/- in the mar 26th. The interest rate is 3.25 - 3.5% on the card. Late fee charges is Rs 350.

I have paid dues in the month of october (around 15 th).. (almost after 6 months)

so, @ 3.5 % interest = 900 31.5 32.6 34 36 38 = 1074.

late fee charge = 1074 350 = 1430

BUT, THEY HAVE CHARGED ME RS. 3700.

How can they charge so much?? Do they charge late fee of Rs 350 every month?? how much will they charge for service??