All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Both parties of the rent agreement are obliged to abide by its terms and conditions. One party of the contract cannot nullify it without the approval of the other party. The meaning of this contract is that the tenant is allowed to rent the house for the period of the rent, and the landlord gets his money. The evidence about this is the saying of Allaah (interpretation of meaning): {O you who believe! Fulfill (your) obligations….}[5:1]. So if you rented this house for a period of three years, then you have benefited by having the right to reside in it for that period of time and you have to pay the rent whether you actually lived there or not. It does not matter if the contract states that the rent is for a period of one year, because the previous agreement was that the rent was for three years. This means that it is a condition to renew the contract annually until the end of the three-year period. Therefore, you are not entitled to the deposit unless you paid the rent for the three year period, otherwise the deposit will be considered as a part of deserved rent. As regards the ruling about not asking for tax relief, and agreed with the landlord not to do so, in order for him to hide his tax situation, and avoid having taxes being imposed on him, there are details regarding the ruling of imposing such taxes.

If such taxes are imposed on citizens unjustifiably, then this is a clear injustice whether by a Muslim of non-Muslim country, because it is taking people's money unjustly. Allaah strongly warned against imposing such taxes. The Prophet said: "The one who in justly collects duties will not enter Paradise." It is impermissible for you to ask for this tax relief, because if you do so, you will cause the government to take money from him without a right and you breach the contract which is agreed upon between yourselves. The Prophet said: "Muslims are bound by their conditions which are in accordance with Islaamic legislations." [At-Tabraani] However, if the government imposes taxes with a right, like imposing them in order to provide basic needs, like security, education, health care and the like, then it is permissible for you to ask for this tax relief. You can take whatever amount they give you, and the previous contract between him and you has nothing to do with this as he is avoiding tax payments. When a Muslim enters a country with a contract (entry visa and the like), he is obliged to abide by its laws as required by the contract, provided these laws do not contradict Islaamic legislations, Allaah says (interpretation of meaning): {And fulfil every covenant. Verily, the covenant will be questioned about.}[17:34]. You have to know that if the landlord buys the property with a loan on interest, this does not invalidate his right to own it and rent it, because the loan after receiving it becomes a property of the debtor and becomes a debt. What he bought with this money becomes his legitimate property whether it is a loan with interest or not. But the debtor is sinful in getting a loan with interest. 

Allaah knows best.