How big is the pot : I think it is 2600 pre-flop (3 * 800 + 2*200). On the flop there's 6000 more = 8600. You bet 1000 on the turn so the pot is 9600 + the all-in which is (3600 - 800 - 2000 - 1000 < 0) I don't get it.

Look at your numbers and you'll get decent answers.