Blue label connect " contact"

I found myself in a contract that I never agreed to. Vodacom asked me to call them and they told me they were supplying me with free airtime in exchange that I use my credit card to buy airtime and data..what is that? How do you just take over someone's account without any agreement? Cancelling that comtract was even worse. My network was suspended and I had to go to vodacom to re register my sim card again. I was soooo upset.