HDFC Bank — Credit Card Outstanding for Misuse

I was holding HDFC credit card and that card got misused though it was with me.I am sure someone used it by Internet for Air Tickets.I raised complaint with the bank for investigating this.The bank blocked my card and issued me a new card and commited that they will investigate within 45 days.When I called up Cust care within 45 days, they said investigation is still in progress.When I called up after 2 mnths, they said investigation was not even started and without the letter in writing, they dont investigate any issues.I then faxed them in writing abt misused transaction but they said since it is after 45 days, they cant do anything and I am liable for the whole amt 18000 Rs.I refused to pay any amt as it was not my fault.hence they put 14000 Rs on hold from my Debit Account and finally withdrew it without my approval.I made several request but they are asking me to pay the whole amount.I didn't say anything against 14000 RS withdrawal as I am working and we dont have time to work legally.But now after six mnth, the bank sending legal notices asking me to pay the remaining amount.I really dont want to settle here as the misused amt was just 17000 Rs and they already took my 14000 Rs and they want rest of the money now which is 20000 Rs as of date.Its really unfair as it's not my fault but customer care's lack of product knowledge.Can someone suggest me as to what to be done here as I have already lost 14000 Rs for no reason.