Do you have an attic? I had trouble finding them in part of my house so I went from above. Drilled a tiny hole through the ceiling right next to the joist on each end of the room and stuck a small nail through it.

Cut it with a sawzall as close to the concrete as you can get, then use a hammer to knock down any sharp edges, then cover with dirt. If you ever need to remove the whole chunk in the future you can rent a jackhammer, or if you’re trying to lift/tow it out you can wrap a heavy chain around it.