Who is liable for a security deposit in CA when a property is sold and only part of the deposit is transferred? Former Landlord?

i bought a house that had tenants occupying the property, in escrow the deposit was 600. Now the tenants claim they paid more, a full months rent on top of the security deposit. Who is liable for this extra portion of the deposit? Do the tenants need to contact the previous landlord since he was the party to the lease? I have documents proving I did not receive the last month's funds.
I just found out when the tenants gave notice almost 3 years later. Am I liable for funds I never received? - Is this your question? Add additional information