After signing a lease with a realty company to take over a tenant's lease, i was not approved following a credit check. Now the company has taken my security deposit but says I "have to" find a co-signer, which I initially expressed was not an option for me, or find someone to sublet the apartment. They will not return my security deposit (which they took at signing), and have insisted I'm legally bound by the contract, but that without finding a new renter, or paying six months in advance, or bringing in a co-signer, they will not let me live in the apartment. They haven't even given me copies of the signed contract, though i have electronic copies of the forms without my signature. Is this legal? What are my options?