You have more than one chiropractor? Exactly what problem do your chiropractors tell you the flat feet are causing?
When I was a kid, a podiatrist had me wearing those useless things. In my late teenage years I started playing basketball. The arches of my feet developed and the ankle bones repositioned themselves (I play defense on my toes). I lost half a shoe size, and have had the smaller shoe size and higher arch ever since.