Warranty replacement iPhone doesnt arrive

I did an upgrade to my phone a while back via MTN Direct (BIG mistake) after a few months the phone became faulty - freezing at least twice a day. I returned the phone (via the local MTN store) and duly received a warranty replacement authorization code. This I was told I must give to MTN direct ( ********** 667) which I managed to do after waiting on the phone for almost one hour. Gave the code and was told someone would call me to verify the delivery details. Needless to say have never gotten a call. A week ago I re-did the call (again 45 mins holding on with that terrible music) - was again told someone would call me. Yesterday I tried to get a status - and was passed to at least 3 different departments - each one not able to assist at all. All said I must phone MTN direct (the above 083 number) What can one do to get them to deliver the replacement phone? Am thoroughly ****ed with MTN customer service