Over Due iPhone Delivery

I purchased (upgraded to) an iPhone 6 on 10 April 2015 using MTN Direct. After some time the iPhone 6 became defective. I then returned the iPhone 6 to the MTN Service Centre in Midrand on 14 July 2015 for a warranty assessment. The iPhone 6 was booked-in on that same day and the warranty assessment was approved on the same day. On 15 July 2015 I called MTN Direct to request a new iPhone 6 and I was informed by MTN Direct that the iPhone was available in stock and in the colour I wanted. Isn't the delivery of the iPhone 6 supposed to take place between 3 to 10 days (ie latest by 25 July 2015)? Every time I call MTN Direct, I'm transferred from one call centre agent to another to explain the same thing over and over again (no clue on what's going on) and then eventually I am told that my iPhone 6 is in the storeroom for delivery! Today is 7 August 2015 and I still have not received my iPhone 6. The frustrating reality is that am still going to be billed for an iPhone that I still do not have and not even using! Is MTN too big to even update customers on delays?!