How did you not notice when you tightened up the bolt? Just curious.
Sound like the bolt was previously twisted or weak. If it went in easily it should come out easily.
Careful drilling and an easy-out should do it like 1958GMCnut mentioned. Should not require a heli-coil unless cross threaded beyond cleanup/tapping or you used to big a bit.
Have pulled out many over the years that were extremely stuck.
