DWP Refusing to withdraw PIP claim

Has anyone had this situation?

Cl was receiving DLA low rate mobility and middle rate care. Cl suffers with epilepsy, which causes memory loss and confusion.
Cl was sent out a renewal form for DLA, however, Cl sent the forms back without completing them as he was attending a funeral and could not deal with completing them.
Cl’s benefit stopped from April 2014 because of this

Cl made a claim for PIP, which has now been sent to ATOS
However, today Cl has received letters stating his Mandatory Reconsideration has been allowed and his DLA has been re-instated at the previous award. 
This is because the Cl had a death in the family.
Cl said he does not remember who he has spoken to or what he has done etc.

I called the PIP office today to see if Cl can withdraw the PIP claim as it was made in error (Cl is happy with DLA)
Explained the Cl has poor memory etc. I was advised by the agent that if Cl withdraws the PIP claim, his DLA claim will also stop.
The agent said their guidelines state claimants cannot withdraw a PIP claim if a DLA claim is live.  However, if Cl did not have a live DLA claim they would allow him to withdraw his PIP claim!!

Can anyone help with how to challenge this?

That sounds right to me, I’m afraid. See Reg 30 of the PIP(TP) Regs, and also this thread: http://www.rightsnet.org.uk/forums/viewthread/5115/

Jon