You can sue the landlord. One party to a contract may not unilaterally, or by himself, change the terms of the contract. Rental leases are contracts. By prepaying 3 months, the landlord agreed i.e. entered into a contract to rent to you for three months at that rate and to not use that money for other purposes. If the landlord breaches a contract in a material or imporant way--and raising rent when he cannot, and using the prepayment money for it, is a material violation--that material breach would let you treat the contract as terminated and recover your unused funds. d on what you write, you appear to have a valid case for breach of contract and could, for example, sue the landlord in small claims court, acting as your own attorney.