Have a beer and think about it!
1) Go get a new one and new wrench.
2) Find a star 6-point American bit (7/16"??) and pound it in. Sometimes grinding the tip concave will turn it into a slight cutter and it'll cut the corners on the way in until its seated. Try again.
3) Try an 11mm hex, slightly ground down. Same thing concave tip. Pound it in.
4) Use a very sharp cold chisel cutting into the perimeter and spin it out. This works! Just don;t dork up the oil pan!
5) Weld a nut to it
6) Remove the oil pan (see step 1 and 5)

7) Be thankkful its just the oil pan and not the differential drain plug/fill plug.
Hope this helps. . .
/73