NHAI — Problem with fastag toll

I was driving from manesae to Gurgaon, and the toll showed the fastag blacklisted. I was told that I would have to pay with penalty if fastag not working. I was made to manually exit the toll and wait for them to assess. In meantime the toll was deducted from my fastag, despite I was given edit manually and waiting for the person so check details. I was lucky to be traveling with the mobile that was linked to fastag, and sms came immediately. Else i would have ended up paying toll twice with penalty. Pls see if it's genuine fault or fastag system or manipulation to charge twice.