Epoxy, if allowed to cure properly, should have held it.
The granite shop I've worked with mills T-slots in the stone, and supplies T-bolts and clamps to hold the sink in place (in addition to a good silicon - the clamps hold the thing in place while the silicon cures). Drilling granite without the right tools is asking for cracks.
You can build a cage around the sink that goes to the floor or maybe you could get away with the cabinet sidewalls to hold it in place after putting some silicon on the edges. This may be the least chance of damaging the granite when it wasn't prepared well for the sink. Getting it around where the faucet and the front may be problematic, since there often isn't much room, but you can probably work something out.
Sometimes, people will drill holes, epoxy in threaded adapters or studs, then use a clamp on them, but doing it to an existing slab from underneath with a hand drill is risky if you haven't done it much...get things cocked just a little, the bit binds, and you'll crack things. Plus, the bits need to be kept wet to work, and that's both though and messy upside-down.