Endless problems with my Samsung S5 mini

I got a Samsung S5 Mini on a Vodacom Contract in December 2014. On the third day it just lost signal and Tiekam's, where I bought the phone did a sim swop. then it started freezing, go blank and just wont work. It went on like this untill February and the phone was sent away. It was the 2nd of Feb. According to the Repair Centre they only received the log on the 24th. I phoned Vodacom customer care on the 9th of March to find out where my phone is, they said it has been delivered at Tiekam's on the 2nd of March. When I got the phone,the Repair Centre replaced the screen and the speaker which there was nothing wrong with. Then all of a sudden I could not hear anybody and they could not hear me. They did noting about the softwear. It was sent back to them to fix the problem and in their report they said that there is nothing wrong with the phone. When we switched the phone on at Tiekam's it had no signal. It was sent away again and now nobody knows where my phone is. I have been paying for a phone I am not using.