[Rust hole]

I started removing the body. I got all but 1 bolt out. several broke which is fine with me but one in the rear that goes thru the wood floor is not giving up! I plan on replacing the wood floor anyway so i kinda cut it away hoping it would give up. Used the floor jack and a chunk of wood but nothing so far. Has anyone encountered this? did I miss something? I count 10 total bolts.

Thanks