Credit Card Fees

On my credit card statement is says if I pay the full amount by 2 August, no interest will be charged. So in July I've paid MORE that the outstanding balance, and still they deducted interest and all other fees. So I've tried to call them this morning - 7 TIMES! and every time I get transferred to another person or department, but before I can speak to someone, I get cut off! This is so frustrating, and I want to know why they deducted the money even If by 2 August I had an advanced amount on my credit card.