Do you have a confirmation from the agent that the PPR was sent via EMAIL/Post Mail? If yes, then you can send an email inquiry to ND office saying that you have not rcvd it yet and you know that it was issued. I know a case where the PPR letter was sent but it was blank without any attachment (PPR letter) and he did contact ND and they were able to resend the ppr email again..
OR If you know that it was issued as the agent confirmed and they wont send another one, send your passport and write a cover letter explaining that you never go it but the agent told you it was issued ( ask the agent his badge number/employee id or something) so that you can reference that in the letter.. this way they know that the PPR was indeed issued and check with the systems and if as you were told it was issued, they will keep ur passport .