National Highways Authority Of India [NHAI] — Toll plaza denied the Fastag and charged double in cash

My Fastag has Rs. 160 balance and still the system at the toll plaza Kochi, Kerala informed that the Fastag has insufficient balance and even after I informed that the NHAI has removed the minimum balance in the Fastag, they did not allow me to pass through. As they insisted I paid double the chares i.e. Rs. 80 (Rs. 40*2) in cash. Hence, please look into the matter and let me know why this has happened. Also, please refund me the excess amount I paid in cash.