Reinstatement of DLA pending PIP assessment

My wife was awarded DLA for life. Last October she was rushed into hospital with a perforated bowel. She was ill for many weeks. While she was in hospital the PIP claim form arrived and when she returned home we filled it and returned it. I specifically requested an afternoon appointment due to her condition but the appointment was made for 8.30in the morning. I rang atos and rearranged an appointment and agreed reluctantly to a 10.45 one. However as we both had flu we were unable to attend that too so I rang atos to explain why. The claim was returned to the DWP who disallowed her pip claim for not having reasonable grounds to fail to attend for her assessment. We asked for a review but they stuck to their guns. We appealed the decision to the Tribunal service. While filling in our grounds for appeal I noticed that the DWP had put the date of her first appointment on all their letters and never mentioned anything about the second one. I pointed this out in our letter of appeal which was passed to the DWP by the Appeals service. They 'reconsidered' their original decision and put us 'back in the game' and said they would arrange for another appointment with atos. I rang the DWP to query whether in view of their new decision they would be reinstating my wife's DLA until her subsequent pip decision. I was promised a reply within three working days but heard nothing until today three weeks later. In the meantime we had received communication from the appeals service who said that if my wife did not receive a new appointment within 10 working days the Secretary of State would have to explain why. The 10 days have now elapsed but we received a call from the DWP today. She was very abrupt and said she had already tried to ring my wife two or three times this morning. This is patently untrue as we were both in from 7 this morning.In the unlikely event we had missed two or three calls it would have shown up on our phone as 'missed calls' and she said she had let it ring and ring. Untrue - we have an answering machine! Unfortunately my wife didn't think to get her name but eventually she grudgingly apologised for not 'ringing back' for so long. She said the DWP had passed her case to atos to arrange another appointment which I presume is due to pressure from the appeals service or secretary of state. She said that DLA could only be reinstated if they had make a mistake. My wife pointed out that she had a letter admitting that had made a mistake so her DLA should be reinstated up to her pip assessment. The DWP would not agree and said this could not be done but if(and she stressed 'if) my wife is awarded pip it will be backdated. Sorry it's so long winded but I wonder if anyone has any ideas on what do next as it seems obviously unfair that my wife should be penalised like this for their admitted error. I am going to ring the appeals service tomorrow and inform them of this latest development as they do appear to be on our side but would appreciate any comments from members who have been in a similiar situation. Many thanks