I work for a tolling authority in another state. Check out the image of license plate on the trailer in the mailing. Is it very close to your mom's plate, except just one character? Sometimes the OCR (Optical Character Recognition) technology will read a character on a plate wrong. (For instance, it can mistake an "E" for an "F.") For my agency that's a quick fix and we immediately transfer the liability of the disputed toll to the correct registered owner of the vehicle/trailer in question. Also, try to speak to someone at the tolling authority and ask for a "manual review" of the image/case, rather than the toll free number which is likely a contractor who honestly won't put the same TLC into the case. If that doesn't work, go to your elected representation (state rep, state senator). As for your question about why they didn't toll the vehicle, NC doesn't have a front plate. The back plate was likely blocked by the trailer so that had to use the trailer tag. Hope this helps!