standard chartered credit card

I've been charged interest on standard charted card even though I made the payment within 3 days grace period but all in vain. I have even shared RBI guidelines with them but no gain. What can be done or if someone else faced same issue?

My salary is 60k and i have amazon pay icici cc 130k (5% utilised) and hdfc bank cc 100k with 60% utilised because of loan Should i attach my salary slip or credit card statement for sc credit card .. if cc statement then which one ? Which is better among salary slip and cc statement for...