Sounds to me like your clutch came apart inside the gearbox, not sure exactly how it's put together but a loose nut, broken circlip or cross pin would cause the outer bell to fall down, preventing the shoes from contacting it, maybe even letting them fall off their mounts. There isn't much you can do to destroy the clutch, other than jam the bit, pin the throttle and let 'er buck, but even that would take a while to burn it out. My money is on a defect when the clutch or gearbox was assembled. Hope it works out for you.
