Is your county animal control department separate from your humane society? In the states alot are..and their animal control department do not have animal cruelty investigators. The humane society does.
Just from their comment of oh i'll talk him tomorrow, should have been a red flag. If you find the cat, take him to a vet. Let them know that you are not the owner of this animal, yet this animal has been in distress for x number of days, yet the owners are doing nothing about it. The vet odds are will contact the humane society.