Malfunctioning device

I was contacted by vodacom via sms to upgrade my contract, I did and received a device that the sales person **** to me about what it can do, so I returned it for a blackberry 9720 which in less than 3 months has been in for repairs on errors 4 times,they sent me a new blackberry 9720 device which is also now in for repairs after not even a week of me receiving it. Vodacom does not want to replace the device for me for a new device which is not a blackberry, so now I'm paying for a device that does not work and is in for repairs most days. The upgrade was done in February this year and its been faulty from day 1. I also got double billed for my old contract as according to them ,I upgrade 2 months to early. Nobody is willing to help at vodacom! I am at a loss for words. There is NO service or answers or help!!!