The pan threads are most likely stripped. The pan usually strips before the plug does. To get it out you can use a screwdriver or something flat like that and "wedge" it under the plug as you turn it. That will usually help get it out. But, if the pan is stripped it depends on how bad it is as to whether or not you'll get a plug back into it. You can find pan taps that *might* be able to clean the threads up, but again it depends on how bad it is. You can also by replacement self-tapping plugs that will create their own threads in a damaged pan but they are pretty "backyard mechanic" and don't always work. I've seen pans "repaired" both ways and people have gotten along fine but either of those fixes would be my last choice solution. The best choice would be a new pan and plug but moeny factors will weigh heavily on that decision.