“bolts came loose”
“go in a couple of turns then it stops”
Sounds like what’s happened is that the bolt came loose until there were just a couple of turns left in, then it pulled the last couple of turns of helicoil out with it.
I wouldn’t try drilling it. Helicoils are very hard and you would still leave the outer part of it in the hole anyway.
Look closely down the hole. Hopefully you will see the end of the helicoil nearest you pulled away from the edge of the hole.
Get a pick or small screwdriver behind it if you have to, then grip it with long nosed pliers and pull gently as you unscrew it.
This is more or less the reverse of how they are put in, so should get it out.