British Naturalisation documents request

Hello folks,

I submitted my application on the 31st of March,2015 and still waiting for a decision.
I requested for my original documents in May and was advised to wait till my application reaches 3mnths with them which I did. The documents were needed for my daughter's student finance processing and my new found job identification because I did not use NCS.
ALl my documents were returned on the 6th July except Our Biometrics. They returned my Original degree certificates, all our passports, my children's birth certificates but they refused to return our BRP cards. I have sent 2 registered letters to them and e-mail without acknowledgement or response. I have also called the helpline severally, they kept on telling me, someone will call me back but they never did. What else do you think l should do? Please help me out. My new employer contacted them on employers' helpline but they never responded to confirm my application with them. Pls, l need advise on what step to take next?
Thank you.
Agbeke Ologbon.