ICICI Bank — Regarding credit card fee

I am a credit card with the bank and for one month, I missed paying the statement amount on time for which the bank has charged me late fee payment and also interest charges. I have a relationship with the bank since past three years. In spite of that the bank feels that because I have defaulted in one payment they should charge me instead of checking the reason as to why I delayed. I had requested and reached out to the customer care executive told that you know because of family emergency, I was not able to pay on time, Request you to reverse and considering that you know my background has been very nice and I have paid all my statements on time. The customer executive told me since you are there with us for the past three years. You should have known that the time to pay is on so-and-so date and you have not paid which is why you need to now pay the penalty what kind of a rude behaviour and services, The bank providing is my question