Barclays bank Credit card
Interest charged even after payment

I have a Barclays credit card no. 4339-5102-9473-6279, with this card I have some purchases in feb.2008 of Rs. 8500/- and paid Rs.9000/-, next month i have some other purchases and statement show Rs. 250/- due but i have some other purchases after statement date which was reflected in the next months statement and total was Rs.818/- but i paid the entire amount of in advance, one month prior and that was also of Rs.918/- wrongly. I made that payment by cheque dated 31/03 and drop tha same on 30/03, as per bank's statement cheque should be drop 2 to 3 working days prior to due date and the due date was 01/04, so my cheque drop date is 30 march which is a working day, 31 mar and 1 Apr is also working days but in the next statement bank chrge interest and late payment fees. I wrote some E mails regarding this but bank refuse to give me reversal after some time bank ask for Rs.200/- to close out the matter I paid the same in cash on 24 oct.and a mail is come to me regarding reversal of charges but nothing is reflected in the coming statements and calls from recovery agents continue to disturb me. I mail the reversal mail to bank but they refuse to give me anything