Continual good cause for backdating

My client logged a change of address with the DWP over the phone. This process takes around 10 minutes and during the phone call the adviser asks lots of questions including questions about housing status and whether the client wants to make a claim for HB. Because all my client was doing was changing addresses he presumed that he had done everything including a claim for HB. He didn’t then make a seperate claim for HB. He moved from a completely different LA.
I have tried to get the transcript of the change of address questions which the DWP advisers use but the DWP have not been helpful. They do not have the actual conversation between my client and the DWP adviser but I hoped they would be able to provide the questions. They say they can’t do this?
Does anyone have any ideas how I can get hold of the questions asked when a claimant logs a change of address?
The case is due to go to a tribunal in November. The backdating period is just over 2 months. Does anyone have a similar case? I can see how easy it would be to think that the 10 minute phone call notifying the DWP of a change of address, particularly because claimants are asked about their housing status and whether they want to claim HB, could lead a client to believe that they had done everything required.
I’ve got a copy of CH/2469/2009 which is useful, particularly on the test of reasonableness, however I need to back this up by using the actual transcript. Help much appreciated.
Thanks.