I didn't pay attention to all the details. However it is generally accepted that you must give 1 months notice before you move out of a leased place, and therefore pay the rent for that month. If your plans have changed and did not move out at the stated time, then yes I think you should be responsible to continue to pay rent for at least a few weeks or until the landlord has found a replacement tenant. You have to think of it from the landlords side too, and that a house with no tenants in it is losing money, and the fact that you changed your moving date would have made it difficult for your landlord to acquire a new tenant for a specific date.