The party do know the purple hand are in Middenheim - Othmayer (a red crown guy) told them so, and his own files (which he took with him when he fled Altdorf) confirmed this. My extensive plot summary in the last post of the character sheet thread explains this!
The party know about a haulage company in the Wynd that is (according to the red crown files) a front for the purple hand.
However, the only purple hand members that the party have met (for sure) are Kastor Liebenrung (who they found already dead), a chaos warrior who was a guest at Castle Wittgenstein, and a wizard in a secret lab in the tunnels below the city (the one with the pet mutant lizard). The cult may or may not know about the party: there's no way to tell yet.
I don't know why you think that you deserve to be beaten up by angry players.
I feel like I'm being excessively mean.