Cannot retrieve a spark plug

I own a 2002 mustang gt and i went to replace the spark plugs to find out that the previous owner had incorrectly put a heli coil in a striped plug socket. Now the base of the plug is sitting below the head and i can not get a socket to bit on to it. I was curious as to what i could do to get it out. Thanks.  

Have you tried a regular 5/8 deep socket ?  They have a little more reach than a plug socket.  

Yea i tried a regular 5/8 deep and still nothing