Bank asking foreclosure charges for closing OD account even though It is not foreclosure

I am trying to close my OD account at Kotak bank .My account was up for renewal on 15th January. I opted for closing my account while i asked for paying all my dew by 1st week of February. The bank closed my OD account from 15th and the account was inoperative while i was charges extra interest for the dew amount until i completed by dew by 7th of February. The bank is charging me foreclosure of 4% on the OD amount sanctioned .We have asked them for documents stating that we are liable to pay the amount for closing the amount but we get no reply on mail .They want us to sign a letter stating that it is a foreclosure which it is not.What steps can i take to resolve this issue and how do i close the account.On top of that the concerned person has even agreed that it is not a foreclosure but wants to charge the amount from us irrespective of whether it is a foreclosure or net.He said that I can keep writing mail ,he will not reply to any mail .The bank is bent on charging money for closing account and is not showing any proof that the charges are applicable.How do i proceed in this regards.