What can I do to help when animal control isn't helping? PLEASE READ!?

There is a horse farm where the horses are 100% NOT cared for and mistreated. They are living a MISERABLE existence and are used only for lesson horses, which is the only time the ever come out of their stalls. Their stall get clean ONLY once a month if even that. Their coat is disgusting and they smell like they're rotting alive. They are also VERY thin! The life in their eyes are gone and they are very depressed. It's really really heartbreaking. The humane society apparently has been out there several times but hasn't done anything but give a warning. I'm only 14 but I'm willing to help these horses in any way I can! I have tons of experience with horses so I really want to help them. PLEASE any suggestions!! I'm desperate! Thanks!