Unacceptable / Disgusting service

I signed a contract via Vodacom on 16 Nov 14 for business use, I acquired a Samsung S5 mini cellphone. Since receiving that cellphone, it has been in for repairs for the 3rd time. The 1st time was 12 Dec 14 at the Vodacom Repairs Centre in Alberton. It was booked in because the screen froze and the phone was inaccessible and the battery was not holding a charge. It was returned allegedly repaired on 15 Dec 14. I took it back on 19 Dec 14 for exactly the same issues that it was taken in for the 1st time. It was returned again allegedly repaired on 7 Jan 15. I still experienced problems with it and decided to take it directly to the Samsung repair centre this time, hoping to get better service. However this has proven to be worse and has become a huge business inconvenience as the phone is used primarily for business. The cellphone was booked in on 02 Feb 15 and to date I have not received any feedback from the service centre and I still sit without a cellphone of which I have to pay a monthly fee for. I find this to be highly inconvenient and highly unsatisfactory. Both Samsung and Vodacom claim that it is not their policy to replace the unit. I want my contract cancelled.