The question is really at what point your lease (and therefore your responsibility to pay) terminated. There are a few moving parts with your situation: the original lease agreement, the potential later modifications of the agreement (per your mentioned "written" discussions with the landlord), and the plumbing issue, which sounds like it may rise to the level of making the property uninhabitable. If the plumbing issue is indeed something under the landlord's control, their failure to address the problem (regardless of whether he can afford it) may be a violation of the lease agreement by the landlord. It sounds like you have been more than cooperative with the landlord up to this point, but if he is going to continue to demand additional payment I recommend you consult an attorney to review all the documentation and craft a response. Alternatively (since the cost of the half-month rent you did live there in February may be less than the cost of hiring an attorney) you might just push back in negotiating a resolution with the landlord, strongly emphasizing that you are willing to pay for the time you were still in the apartment but that you will not be responsible for anything further as you complied with his notice request (potentially when you didn't have to) and because the fault lies on the landlord's side for not properly maintaining the property and thus violating his responsibilities under the lease (and forcing you to have to move and incur the costs of a move). It sounds like he may be bullying you a little bit to try and get a little more money, you just need to remain firm in your response. However if he remains determined to press the issue you will want to consult an attorney to fully review the documents and advise.