National Highways Authority Of India [NHAI] — double toll collection at toll plazas

I have noticed that few toll plazas were deducting toll twice once through fast tag and manual as well. Those toll plazas say that fast tag is not working at that time and they make us go through the normal gate which is also fast tag enabled thereby deducting toll while passing through that as well. The message for fast tag comes at a later time by when we would have gone at least 10 km. I myself came across such instances some 3 times. My vehicle number is ka01mn4036. Latest incident happened at devanahalli toll plaza near bengaluru airport. Kindly check these discrepancies in the system.