It has happened before as well when ICICI's automated mail didn't work.
If you go the legal way, they will just put up their MITC where the wording would be twisted in a way which would still make you the defaulter. Ask them nicely if they can reverse those charges and not report late payment to CIBIL.
Request may work but don't think you can do anything legally. When did it settle? 3rd or even later? If due>500 & settlement is >7days, it's doubtful they'll even consider it.
As due date is fixed, it's also your responsibility to check.
In case of complaint, they'll pull up something from mitc. Have you checked everything? Mail/msg/notification in app/netbanking.