Contact customer care and ask them to send account closure link. Once you got the link click on it a form will open. Fill and submit the form, your account will be closed within 3 days.
Keep in mind they will try to convince you to not close the account. And may even say that it is not possible online. If so, say that one of your friend closed the account by this method.
If they still deny wait for 1 hour and call again eventually someone will do it.