Tab Faulty

My Son brought a tab by Vodacom in Promenade on Friday the 25th September 2015 when he got home he saw that the tab is not working properly on the 26th Saturday Morning he then went to Vodacom to complain they told him their technician is not there he might come in later he waited a while then afterwards left he then return to Vodacom on the 27th Sunday morning and spoke to Nadeema he explain to her that the phone is still not working he would like his money back as he came back to them within the 7days period she told him they cant refund him then he ask that they should exchange it if the other one cost more he will pay the difference then it was also a flat no how can you pay for something that is not working properly