Bad Service in Cellphone Department

So my sister bought a Verse 7 inch tablet from CNA Pinecrest Mall in Pinetown in 3 weeks the tablet started giving her problems (freezing and required being charged 3 times a day). She then took back to the store and was helped by Siyabonga the Cellphone attendant and he fiddled with the phone and said it needed updating which he evidently did it for her. She went back home hoping the phone was ok but it turned out to develop more problems and she took back again after a couple of days and he said she was the problem and there was nothing wrong with the phone. At the time when she was going to CNA about 3-5 people had brought in the same tablet which meant they were really faulty. After being given the run around my husband and I went to the shop and demanded proper service and the phone was taken in and we were told it will be ready in 4-6 weeks. After 5 weeks Siyabonga called my sister to come fetch the phone and when we arrived at the CNA Siyabonga was not there and we we told it was lie the phones are not back, WE WANT OUR MONEY BACK AND TIRED OF BEING TREATED LIKE THIS. The managers have NOT helped us as well. Siyabonga is also NEVER at work and we then turned back. HELP HELP