Selling and Marketing

I am so unhappy with Vodacom in regards to phone calls from them selling me insurance, contracts and data. If I need assistance I will call Vodacom myself. After I tell them I am not interest in what they sell they just keep going to sell more, why is there a consumers act if they do not adhere to it. I have a few contracts with them but with current calls I receive from them not stopping I will need to cancel and look at other options.