Exchange cell phone denied within 7 days

hi my Name Is Lawrence Radebe I bought a cell phone last week saturday 23, 2021 Premeo S8 at Ackerman's Jabulani Mall its gave a lot of problems during last week I went to them today 31Sunday 2021 I explain to them when they ask I didn't returned it yesterday , because My mother past away 2weeks back and yesterday we were cleansing for 10 days Saturday I was not allow to leave the house till the next which is Sunday they telling me that 7 day has pass and I ask how do they calculate their 7 days since they dnt specify on the slip and why should i repair a cell phone that broke and given me problem within 7 days its means its pup phone so i want another cell phone i wont use a problematic phone. They insisted i book it for fixing so wana know, how this work or how do I get money back since Im not happy unless they are selling used cell phone. I even have death certificate of mother to prove why I couldn't go to a shop yersteday could they just help me