If you have a "Dremel tool" with a reinforced cut-off wheel, or even a hand drill, (those cutoff wheels and mandril are $5-$6).
Cut flat sides on 2 sides of the head and try the pipewrench again. It's gotta work. Last resort, drill out the center of the plug and drive an "Easy out" into the hole...Last, last resort, drill out the whole plug except the threads and rip them out with a chisel. Auto parts stores have generic oil plugs with expandable seals.