National Highways Authority Of India [NHAI] — double toll fee within 50 km

I'm Sambath Kumar the serving soldier of Indian Army and also I'm from Kallakurichi when I'm moving by a car from Kallakurichi to Villuparam there was double toll fee needed to pay in between the short distance. Distance between Kallakurichi and Sengurichi is 36 km but should need to pay double tax why this kind of roll should be followed by a toll service