Airtel pre-paid
Top Up Validity Problem

I have recharged with RC 46 by which i can call all STD Calls at 75 paise per min. for 30 days on 10/8. But today i.e; on 31/8 when i called a STD Number, i have been charged Rs1.50 p per min. I have talked with Airtel Customer Care, But, he didn't respond properly.