New DEFY appliance impossible to exchange

I recently purchased a Defy GAS stove from New World, Menlyn. I did not install it. I got a professional GAS installer to install the unit. The installer identified that 2 of the 5 burned are non functional. I wanted to return the unit to New World, but apparently that is not possible. A service call must be logged at Defy - and they will send someone WHENEVER to come and have a look at the unit, before it can be exchanged!!!!!!!!! Question: Why did the retailer not point out this fact???????? Question: Why, if a certified installer identify a fault, it cannot be exchanged, and when is it mentioned in the T&C's No more DEFY EVER !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!