Contractor vented bathroom vents in attic, now I have mold. Is he accountable?
Venting to the attic is never correct, and was not good 'workmanship' even before the 2006 IRC cycle.  Even if you asked a contractor to vent to the attic, they should have refused, or made you sign a waiver.

Your first step is to research the contractor claims process in your state.
Your second step is to contact the contractor and explain what happened.
Your third step is to contact the bonding company of the contractor: they have teeth, if need be.

You paid to have fans routed to the outside: the contractor should be liable to finish the job as specified, and to pay any consequential damages for failing to do so.