Policy not paid our - 12 years ago

Hi there,<br> My father passed away 12 years ago and had a Life Insurance policy for many years. After his death (died of skin cancer), my mother (married at the time) was told that she has no claim on the policy as my father did not inform them of his illness before he died. He had a medical examination when the policy was taken out which proved him to be in good health. Can you please assist me with this as I would like to take the matter further as my mother had no money and could not afford legal help at the time.