Same thing happened to me when putting in the Eibach Pro Plus kit and AGXs. It broke off right at the head, had to beat out the factory strut, drilled a new hole in the old bolt, broke 2 drill bits before I could even get an EZ out in it, then broke the EZ out, had to drill little pilot holes around the EZ out to get it out because you can't drill through it. Finally decided to drill out the whole darn thing to 1/16" bigger than the original hole, ended up drilling out the threads and all and running a stainless bolt/nut with a couple flat washers to bring it out to where it was easier to get to and a lockwasher. So easy to torque it now, or take it apart, etc. The front end of my car has been apart 4 times now. One more time to go.
The whole mess with that fork took about 4 hours one day, it sucked, nowhere near me (Newton, IA) had a fork available on short notice.