Vodacom giving other people's numbers to new contr

I received a new phone and sim on Friday 18/09/2015. After activation of sim I have been receiving calls from people I don't know. I received a call from a person asking me what am I doing with her daughters phone, I then explained what is happening. I phoned vodacom and the lady says to me that this maybe was a number in use, but doesn't work anymore. However the number was still in use on Friday when I received the new phone and sim. The lady at vodacom says If it bothers me, I can go to a vodacom store and ask for a number change. As if it's my fault. I am going to send vodacom the phone and SIM card back if that's how they do business. So vodacom get ready to receive your phone and sim back, because this is unacceptable!!! And I'm canceling my contract tomorrow!!!