Credit Card — late payment charge on late payment charge

Address: Gautam Buddh Nagar, Uttar Pradesh, 201301

Hi,
I have an sbi credit card for last 3 years and i am an excellent customer at my payments.
I was ill and missed paying a very small amount of 699 rs which got rolled over to next month with a late payment charge out of the 54000 ipaid in my previous statement.
Now as soon as i came to know of 699 i immediately paid a charge of 699 rs and requested for a reversal of late payment charge. The request was raised and probably got rejected.
In meantime i travelled abroad for work and now the amount became 3000.
I immediatly requested again and on refusal of any action by sbi customer care. I suspended my card for a settlement.
Now my question is is it legal to charge interest and late payment charge on a late payment and interest.
It looks illegal to me as i am aware interest on interest is not legal anywhere in the world.
I am not sure how to settle this now. Is it that in order to settle this i require to pay the 3000 which only comprise of late payment and interest charges or they spoil my credit report.
Or do i have any options which is less hectic and not as time consuming.
Sbi is a govt bank but i think the charges made are unfare for me.
They charge me without me purchasing any credit from them directly.