You have several options. You can pay the rent and sue the landlord for breach of the lease agreement or you can withhold the rent. If you choose the latter, the landlord will presumably start an eviction action and you will have the opportunity to have a habitability hearing after you post the disputed amount into Court. Thereafter, the Court may grant you an abatement as a result of the lack of habitability. Should you have any questions I suggest you contact an attorney.