National Highways Authority Of India [NHAI] — Fastag system loopholes and cash loot

There are toll gates, especially on the state highways which force you to make payments by cash. What these people do is, they keep the fasttag lane open, so you naturally go to that lane(my car is fasttag enabled and has enough balance).
After going there, they say that it's low balance and when I say I have enough balance, they reply back telling that it will take 20min to reflect. So, you can pay by cash. And now, if I choose to pay by cash, they claim 2x money by cash. For example, the toll was 35, now that i pay by cash in fasttag lane, now I am paying 70.
Note here: I already had a fasttag that was active and that had enough balance (200+).
This is a new technique by which these people loot and cheat us.
NHAI thinks that they have a clean system.

This issue is with Vallam toll plaza on NH 234 at 80/600km.