Pension credit asking for money back of late mum from 2002

[rebeccahmum2]

Can any one help long one sorry but mum passed away 17th July 2015 received pension credit disablity and maintance of ex husband of £400 a month.
Received letter from pension credit advising not to touch esatee in August 2015 rang told standard letter and gave them a break down of her esatee wich is only made up of her property not money in the bank.

Received letter 6 weeks later asking for bank statements from 2002 when she first claimed pension credit. She didn't fill the forms in on receipt of pension credit she hadn't claimed anythink until turning ill and wasn't the best at filling in forms . They are saying that the maintance wasn't declared. I can not see my mum not telling them as she had no reason not to. I sent in statement and received on 9th Feb 2016 as you can see this has been going on for months with no nearer to what we owe or any closure. When we call they will not tell you anythink last time I called I was told it would be 10 weeks but then told that they could not give a time frame we are now 14 weeks from the receipt of sending bank statements and 10 months from receiving there orginal letter! Has any one experience of this . We just need some closer and able to morn our loss with out this hanging over us.