A large bench vise is so very useful in a workshop. Head to the co-op, or better yet, get a large vise and bench. This will not be the last time you need it. If it moves (twists), it will come out. I did have one (out of about 50) that twisted but did not come out. I ended up having to drive it in about an inch (risky move). Apparently it was hung up on a chunk of corrosion. It came out immediately.

I cannot imagine attempting this without a vise. You need a vise holding the post still while you twist and pull upward simultaneously.