Sharing my details with another company

I have been with Vodacom for around 17 years now and have 2 contracts. <br> A company called Mondo have been phoning me (7 times!!), saying that they have got access to my Vodacom contract details. <br> <br> This is totally unacceptable. How can a responsible company like Vodacom share my information with other companies. I would like to see where or how I gave my consent to share this kind of information.<br> <br> Please make sure that I am removed from their database.