I think I would start by looking up the rules for your area. In many areas, the requirement is only that “shelter” be provided, which it sounds like it may have been in this case. If the dog doesn’t appear to be underfed or in poor health, the Humane Society may not be able to get involved, in which case there might not be a point to calling. Unfortunately, just because people keep their dogs in conditions that are not up to our standards, it’s not always illegal