Very disappointed customer

I bought a phone last week Tuesday at MALL OF AFRICA and noticed it had malfunctions and decided to return it to the shop while I still had the 7 day warranty....now explain to me why my phone was booked instead of being exchanged like the 7 warranty rule states..what's the point of giving the 7 day warranty rule to customers if you know very well it doesn't exist..what nonsense is that ....why let customers buy your products with a farce policy you very well don't implement..