LAPTOP TECHNICAL ISSUE

I upgraded one of my contracts with Cell C on the 23/02/2019 at Golden walk in Germiston. I received a HP 15 laptop and thank you. it was 10 min before the shop closed and I was advised by the consultant Thabiso to start up the PC at home. I left the store and guess what? the PC was not working, I attempted to return the device the next day 24/02/2019, they couldn't pick up the issue after a whole hour and told me they can exchange the device however their technical department is closed and they cant help, 'I can always bring it back during the week'. However they will be closed on Monday, I can maybe try Tuesday . I work 08:30-17:00 and wont make to the store before they close, never the less, I made arrangements to leave work at 16:00, little did I know that Ill get to the store at 16:58 and find it closed??? I was informed i can make other arrangements to send someone to exchange it, they just need to bring their ID and mine, I would like to confirm those details however they have not answered their phone the whole morning! moral of the story, how do they send me home with a device that has a techincal issue? i cant go to another branch because I left the original box for convenience. I was advised i can only bring back the lap top for exchange with 7 days counting from the time I took it, that is till Friday? Please help!