National Highways Authority Of India [NHAI] — wrong collection of fee at balibhasa toll plaza

Address:

Balibhasa tollplaza. Kharagpur

Today i crossed the toll plaza (Balibhasa tollplaza) with vehicle no. Wb34ac8146 at 10:01:43 (Dt.12.08.2020) towards kharagpur by paying rs70 cash.
But on the same day now i returned at 15:57:52 hrs. They charged agin rs 70. Which should be rs 30 as per rate chart.
Finally toll plaza took rs70 cash from me.
Why it is happening? Please see the matter.