MTN customer service is the worst!!

I was due for an upgrade and did the whole process telephonically through the call center. Recvd my phone(Samsung S6 Edge) which was faulty and they arranged for it to be collected. The collection on its own was very fast(next business day to be exact). Now I have been without a phone for 5 days and MTN could not care less about this inconvenience, Zama keeps promising to call me back and never does until I have to call again to follow up. Requested to speak to their manager whom I am always advised is not in his office(seems he is never ever in his office which is a disturbing factor on this own) what is he there for if he is never available to keep check on his staff and take our calls as customers with concerns. Silindile the supervisor explained the same thing that it takes up to 10 days for the whole process of them to acknowledge receipt of my phone. Now they only thing I have been asking from MTN is to cancel this contract so I can go and buy a phone and port my number if I need to and they are refusing as they have not yet received my phone from the courier company THEY sent to collect from me. Is this really MTN service to their long-lasting customers. I am really appalled