Broken Bolt

File down flat use center punch to dimple center EXACT center. Get Easy Out sey drill recomender nhole install easy out PRAY try and remove. If failes or Out brakes keep drilling one size up at a time until you see threads. The use thread chaser to clean out rest of bolt. If this fails get Heli-Coli drill recomended hole tap insert Tine and new bolt.
Good Luck