Buying a phone that never work at all

Good morning hope you are doing well, I'm writing this email to you as I need your help, I bought a phone from foshin at Cresta the phone died within a month and I brought it back twice to the store asking for a new replacement as I'm currently paying R800 every month for the phone the lady from store said they not going to replace it the company that makes it must replace it and she gave me this call center number which I can't get hold of anyone I'm paying for the phone I don't have every month and I have no other phone to use as I'm no longer interested in that one as it keeps on giving me the problems all the time so would you please help me I need a new one and will really appreciate your help Thanks.