I want a refund

In April I got a phone at vodacom repairs cresta mall as my phone had a problem only to find out that the samsung j100 that I got had bigger problems I have been in and out of the repairs shop just to get it fixed but yet nothing has been done, they have updated the software more then 3times and that phone still gave me a problem 1. It was slow and freezing <br> 2. It showed multiple screens when I had an incoming call 3. It was automatically going back to menu when I open an application 4. It was stopping my music and. 5. I was couldn't swipe it to unlock the phone. So in December I told the repairs shop I don't want that phone as it is useless to my needs I want an R number so can claim my cash, it was even on the report and yet samsung is failing to give me feedback on the process on refund or R number... Its the festive season and my family and friends can't get hold of me I need to know if is the anyone who can assist me with my issue or do I have to call speak out to help in this situation... This is unacceptable how a customer service business can deliver such poor service. I need a solution to this matter.