Standard Chartered Bank — unauthorised credit card charges

I have been using Standard Chartered Bank Credit Card from past 8 to 9 years. In the month of January 2019 I saw a B2-OVERLIMIT fee of Rs. 599 on my card. I immediately called the customer care and enquired about this charge, they informed me that, since I have utilised full limit they have put this charge. I asked them -
a) Why they let my card go over-limit?
b) Why a customer is not informed when the card is about to reach limit or, inform that they will be charged over-limit fee. so, that customer could use the card judiciously.

They told me customer can go and check their max limit though netbanking and utilise the card as per the prescribed limit. However, they took my request for reversal of charges and after two days, I received the message that the charges are valid and couldn't be reversed. Please note my bill is still not generated by this time.

Now, my bill get generated on 20th Feb 2019 and payment due date is 13 March 2019 with . Today 25th Feb 2019, I logged to pay the bill, I again saw a B2-OVERLIMIT fee of Rs. 599. They charged Rs. 599 twice, one on 28th Jan and other on 20th February. I called them and told them to reverse this unauthorised charges. After so much of discussion and putting my point, even though they looked convinced with my argument, they told me they tried to reverse the charge but their system is not allowing saying, it a valid charge.

What does this tell, a system being made to loot the customer. You should have never allowed any purchase to happen beyond my prescribed limit. You should NOT charge anything to the customer without informing the customer. Your customer care executive should have informed the customer that you may be charged again, so forget the bill due date and pay the bill. Complaint No. is '[protected].

Standard Charted should look into this matter, I'm no place to go with the reversal of these unauthorised charged. Do not loot your customers in the name of over-limit fee when they have not asked you to allow any such transactions. Please resolve this if you can or, you lose trust and a customer.
Thanks, Rakesh