National Highways Authority Of India [NHAI] — cheating at toll plaza surathkal on nh 66

The return toll at this plaza for a car is rs.80/- (Return within 24hrs.).
We use fastag to pay tolls.in spite of returning within 12hrs. We are charged rs. 50/- one way and rs, 50/- on return. We come to know about the amount deducted through an email or sms which we receive 4-6 hrs after passing through the plaza.
This is nothing but day light robbery of law abiding citizens who have shifted to fastag well before deadline.
The legality of the plaza itself is questionable as it is within 20km from one at hejmadi on nh 66