National Insurance Company — Health Claim Denial

My husband's health claim has been denied ny Medi Assist and National Insurance for reason as Genetic Disorder not covered.
My husband was suffering from RENAL CELL CARCINOMA WITH LIVER METASTASIS, HIPPEL LINDAU SYNDROME.
This is not genetic and we have provided treating doctor's letter with clarification that this disease is not genetic.
Still National Insurance is not considering the claims regarding to this disease.
3 claims claims have been denied by National Insurance for the same vide
Claim no. 20341389 in August 2019, 24037475 in March 2021 & 20275449 in oct 2019.