You have been gazumped. Unfortunately, the only available remedy is to restart the game, which I don't want to do as it has taken so long to get it started in the first place. And there would be no guarantee that another gazumping would not occur.
Many people, myself included, are desperately hoping that Illwinter will give us some protection from gazumpers in the next patch.
In the meantime, your only alternatives are to play the broken position, or go to AI.