a starter bolts broken inside how do i get it off

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lets see my car hasnt ran for a while now and the other day i bought a battery i tried to start it but when i did it soned like metal scrapin metal real loud i asked about that the other day and someone told me it probably has somethin to do with my starter and flywheel well today i took the alternator out haad it tested and it passed then i tried to take the starter out to have it tested i had it almost out except for one of the bolts was already boken off to where i couldnt get it with any of the tools i have i tried to push it through and tap it with a mallet like autozone said but im havin no luck at all what could i do to get it out please help me :(