Ex-Gratia payment?

I have seen a couple who have had a catalogue of appalingly bad advice from the Jobcentre about what benefits to claim.  I am trying to work out the best way to approach their case.

They moved in together in February and at that time, he was working, and she was claiming JSA.  She had recently taken on parental responsibility for her 1-year old nephew but at that stage had not been able to claim IS, as was still waiting for Child Benefit to be paid.  When told that partner was now living with her, the local Jobcentre told her she could continue to claim JSA as a single person.  As far as I know this was ibJSA not cbJSA.

In March his job ended, and at around the same time her CHB started and she was advised to claim IS by the Jobcentre.  The IS was paid under the lone parent route at single persons rate, even though clearly she was not a lone parent, as she was living with her partner.  I believe he was advised to make a separate JSA claim in his own name when his job ended, but the only money that was actually paid to them was her IS claim. 

Eventually at the end of May they went in to query matters again, and finally someone advised them that in fact he should be claiming JSA for both of them and she should withdraw the iS claim.  Appparantly they only got this advice because someone overheard another member of JC staff again incorrectly telling them that he would have to claim JSA separately! 

They hasve asked if there is any way to get back the money they lost out on by only being paid at the single rate during the time between him losing his job in March and the start of the JSA being paid at the couple rate from the end of May.  The problem is I am struggling to see a way they could do this under statutory provision.  I am assuming mistake as to the material fact that they were living together won’t help, because there was no actual entitlement to IS for them as a couple, and they have already requested backdating of the later JSA claim, that was refused because neither of them was signing on during the period in question. 

Is it worth trying to challenge the JSA backdate refusal?  Or, if it is going to have to be an ex-gratia payment how do I go about requesting this?  I have calculated that even taking account of the fact that she would have been overpaid JSA during Feb and March while he was still working, thay have lost a net amount of about £150 due to getting the single rate rather than the couple rate between March and May.

That’s what I thought, thanks Duncan.  Do I write to the local DBC to request this?