Vodacom leeching off its clients

Vodacom once again stole all my airtime. I would never advise anyone to take out a cellphone contract with them . I thought the law states you may not take my airtime that i paid for if my data is finished . All their notifications are delayed . I get the message after 200rand of my airtime is gone . Is that how you treat your clients . My contract is R700 monthly and you still want to sponge off people.