refuse to pay out claim

my dad has a dread disease which standard bank refuses to pay out on the insurance.We have submited all doctors documents which shows it is a dread diseases. My dad disclosed that he has been dignosed with cancer before taking this insurance, they said if anything wit cancer they will not pay out. After sending in the claim it came back rejected and on their letter it states that they will pay out for cancer? Now he has a lung diseases which they do not want to pay out they say they do not cover that, but when my dad asked the consultant they said they cover all dread diseases thats y my dad accepted that insurance, but now its a whole different story with them.