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I am guessing these are Aluminum , and you tightened them down a little too much , the Aluminum ones don't take the torque like the steel or Titanium ones do ..... Unfortunately the only way to get them out is to drill a Pilot hole and use a Easy Out/Screw Extractor ,
much like you have attempted .... the only other way , is to try to drill dead center , and keep enlarging the bit till the bolt is paper thin , but not enough to get into the threads , it may back out easier then , then either try again with the Easy Out , or use a pointed pick or something small to work loose the threads .... , some of those extractors work like a drill and cut into them , then you reverse the drill and it will back right out ..... unfortunately , that is the only solution outside from drilling it out completely and buying a Heli-Coil kit (which would come with the correct drill) , and replace the threads with a insert , but being it is Aluminum , you should be able to get it out , it just may take some finesse ...