Did your father leave any other assets?
What was the relevance of the account only being opened 3 years ago?
It doesn’t matter why he saved the money, he has to declare it and if his saved money was over the relevant amount for any benefits he received, then he is no longer entitled to get that means tested benefit.
Hence, it may be that the Benefits people will want repayment of the benefit. If your father left no assets, then the debt dies with him.
Can I clarify anything for you? Please rate the service positive so that I get paid. We can still exchange emails. Best wishes. FES.