Standard Chartered Bank — extra charges on credit card

I made a transaction of rs10, 998 on 26th dec with my standard chartered bank credit card. By 23rd jan, i made a payment of rs7478 and was expecting a refund of the remaining amount of rs3520. The refund transaction was done on 26th dec but was credited to my account on 11th feb. My bill due was rs3, 520 and the due date was 18th feb. By 11th feb, all my outstanding amount was paid as the refund transaction was credited, however, the bank has still put a late payment charge of rs590 on my account and say that it is valid charge.
This is simply fooling and looting customers by not accepting refunds/credits as a payment method. They say that i should have made another payment of rs3520 to avoid late payment charges. This would mean having excess amount to be paid for my credit card transaction.
This is simply pathetic service by the bank. I tried to raise a complaint about this and every time i would be told that i will get an update in 48hours. And after every 48 hours, they would say they don’t have any updates on the complaint and would take a new complaint. After struggling with them for over 8-9 days, they finally rejected my complaint saying that this is how it will work and i will have to pay late payment charges. This bank is simple fooling people and taking away their hard earned money. I have closed my credit card account with them and would never want to deal with such a bank in future. Pathetic experience.