Disgusting service on a new iphone that is an out of box failure

I upgraded to a new iphone 16 on Saturday, the 21st. The phone was problematic from the time I tried to access it and I returned it on Sun, the 22nd. The store also confirmed it was a problem and said they'd get it assessed as per out of box failure. I called MTN today and they said it was only picked up today on Wednesday and that it would take TWO WEEKS to assess it. They didnt care that I dont have another phone or that I am paying for the upgraded phone contract and sit without a phone for up to 3 weeks. This is unacceptable and poor customer service. Where is the CPA that states if something is not working, you replace it? I'm disgusted and considering cancelling my contract in it's entirety with MTN.