Pretty Amazing Forces at Play

Good thing it was "old" and "deteriorated." This is probably what you are dealing with http://www.macleanpower.com/products/item.asp?ITEM_ID=2071 If it was augered into hardpan or dense clay, good luck. Next time (if there is one), try digging down a bit. You might even be able to "un-auger" it and reuse it to hold the barn down in the event of a tornado 🙄

If you take 20 of them out of the ground, 10 will unscrew out, 4 will spin because they were pulled hard enough to flatten the screw part so it won't unscrew itself, 4 will spin because the weldment broke on the sheet metal screw and 2 will break down below.
We found it easier to take the backhoe and dig down to get them out.
They are in about 3 & 1/2 feet if I remember right.
I remember once there was a Utility truck down over the bank and it rained so he couldn't get up to the road. The truck up by the road could not hold him on the winch. Finally he swings the drill around and screws in a 12 inch anchor that was used on the high poles. Hooking the winch line on that they were able to winch out the stuck truck.

I have put in many of them. There are a couple of different styles, Some screw in and others expand at the bottom of the hole. I can't remember the rated strength but we always used 60,00 lbs tensile strength cable attached to them.
Just dig down and cut it off with a torch or a grinder. You can do it with a hacksaw too, but it is more work.

Goodluck

Biggastractor