All is not lost. Actually, it probably is 🙁
So, my thread on the same subject can be found here. I’ll cut to the chase – I bought a carbon bike and discovered that the post was seized. I tried everything and anything that might work, but in the end I paid a local indy mechanic to painstakingly cut the thing out, which he did and the bike has been fine since then.
The long and the short of it is that if it’s as seized as mine (which is might not be, to be fair, it won’t come out without violence (i.e. a hacksaw) and don’t be surprised if none of the other suggestions work.
Personally, I think the most effective non-destructive method is freezer spray down the inside, which will shrink the metal post but leave the carbon frame largely unaffected. Then get the top of the post in a vice and twist, but be aware that if it’s as seized as mine was, the frame will snap before the post gives out, so be careful about the amount of torque you apply through the frame.
If you’re based in Yorkshire, and still stuck, drop me a PM and I’ll put you in touch with the chap that fixed mine 🙂