all data gone after two weeks, third month in a ro

3rd month in a row that data all of a sudden dissapears. Previous 2 months it lasted 17 - 19 days, this month only 9 days for 5 GiG to dissapear..... I only use data after hours. I know of all the stories op auto updates etc....everyting is switced off....Vodacom, I want you to rectify this NOW. This is absurd. I see it as theft of data. Give back my data