Airtel — unable to call on few numbers

Hi, i am customer of airtel from last 9 to 10 years. But from last 15 to 20 days i am not able to call on few numbers. Mostly bsnl landline number and mobile numbers. Whenever i try to call within a fraction of second or even less then that, my call will cut down with a message displaying 'call failed'. Today first time i compliant regarding this issue to airtel customer care but to my surprise instead of helping with or solving my problem they told our network is good in your area and we cannot take a complain for this issue. I was literally shocked with the way they behave on call and were not ready at all to help me.