No matter how much a person spins around, the block direction is still the same. So down block should work just fine. My strategy vs. most 2 direction polearms is to just hold down block and wait for the block noise. Since their upswings are slow and obvious it is easy to switch your block if needed. Only thing to be careful about with this strategy is kicks but not too many players are very good at kicking.
If you are sure you are holding block and they are hitting you with thrusts, then it might be because they have gotten to your side or around you. Try to keep them at the center of your screen when you are blocking.
