Pep bought me a sim card.. Service provider says doesn't recognise number and they not replacing it

I bought a cell C home connecter flexi prepaid LTE at pep only tu get home and it said it was not registered.. Tool dim to next cell c shop they said I need to taken back to the pep stores. In this pep they telling me to go to cell c again and not sorting out my issue.. It's a week now and I don't understand why they not sorting out what seems to be a simple issue