For all I can guess you broke-stripped the brazed part of the frame type of seat post binder .
since you left that out.

Want to Bodge with hose clamps, Buy 2, I agree .. 1 grip the post above the frame ,

the other squeeze, the frame around the post together they should handle your weight .


I have used a double clamp scheme just to stop slipping down , these are made for purpose,
rather than hose clamps ...