Assuming the hearing officer was correct, and that your vehicle was towed pursuant to proper signage, ordinances, and state law, then you have no valid claim. The Vehicle Code does not exempt broken down vehicles from impound. In fact, if broken down in a place where it can impede or obstruct the safe movement of traffic, then there are additional authorities that can be used to impound such a vehicle.
Unless there is some valid argument you can make that the area was not properly signed and posted, or that no such ordinance authorizing an impound exists, I'm afraid you're going to have to eat the costs.

