You should have bronze/metal cups built into the pool deck that the ladder ends slide into. Assuming that is metal, and the cut off ladder tube ends are still in these cups, you could spray some penetrating oil on them, trying to get between the deck cup and the cut off tube. Wd-40 would work in a pinch but there are many others (like pb plaster, kroil). Let that sit for 30 mins or so, then try and break them free with a chisel and hammer. You could get a blow torch and heat it up, then try and tap it with a hammer or chisel,, trying to rotate it in the cup,, once it breaks free pull them out with a pair of pliers/needle nose pliers.
I'd be upset,, good ladders are expensive. I like the SR smith commercial ladders, top notch.
Another alternative would be to buy some metal pipe (maybe even PVC pipe),, that you could fit into the existing cut off stems,. the other side would go up into the cut off ladder, and that would hold the ladder in place but that would probably be sloppy looking and leave some jagged edges, unless you filed it down a bit to make it look acceptable