Legal Question in Business Law in California

A lien may not be enforceable, but you still can sue who hired you.

Your question does not make sense. First, you can't do work for "the bank" and "a contractor." Were you a subcontractor to a contractor who had a contract with "the bank," or what? Who did you have a signed contract with? Second, banks don't hire contractors before they foreclose. So who did you do the work for, and when did they own the property? Without that information clearly and correctly stated, it is impossible to answer your question.