Rogue Estate Agent in London...?

I signed up with an estate agent called The Property Bureau. Property bureau has caused me many problems. They got some tenants in for me last August. The tenants gave PB their deposit money and first months rent. PB only gave me 3/4 of first months rent. PB did not give me deposit as I was aware that this new government scheme had come into force so I didn't chase this. 10 months down the line I have not got rest of first monhs rent and I have no idea what PB have done with deposit. The tenants are leaving and have not paid there final months rent as they say that I need to get money back from PB. Surely this is their responsibility. Getting this money back from PB seems highly unlikely, but surely this is tenants responsibility as they didn't give deposit to me they gave deposit to PB so they should do chasing. Please Help!!!

If you can quote any legislation which clarifies this matter please do.