Paid up letter settlement letter

My husband had a contracts with cell c few years ago it all paid up and settled he phoned for his paid up letters they told him they dont have any information about him then he phoned again then they tell him to go to his nearest cell c store they will issue him with it he went there and then they said they cant help him he need to call cell c he phoned again then they ask him a few security questions he then answer what they ask then they said he had failed the security check they cant help him but he did answer everything that they ask correctly they ask how many accounts he have with them he said nothing because he paid them and closed the accounts so he cant have accounts anymore please help any one