i tried soaking the pin with a good penetrating oil like LiquiMoly CERAMIC RUST RELEASE. Then, you start drilling out the obstruction with a jeweller's grinder on a flexible drive. You'll never get a regular drill into the tight space. Bunnings have a Super Works rotary tool kit which is quite cheap and has a small flexible drive that will get you started on clearing the debris out. Problem: the small collett on the drive will only take a drill bit of 3mm.
But once you have a clear hole through, you can start enlarging it manually with a rat-tail file or a hand held wire file/saw like they sell for campers in two dollar shops. But keep the work wet with LiquiMoly at every stage.
Probably, the compression pin has severed at two places where the three lobes of the door hinge meet. Two lobes are on the door and one lobe is on the A pillar. Plus, the pin rusts onto the corresponding section of each lobe and fuses with it. It's the worst, laziest, cheapest design for door attachment ever conceived. Holden never meant the door to be removed. Ever.
