WORST SERVICE I HAVE EVER EXPERIENCED !!

In December 2017 I contacted MTN to find out if my son was due for an upgrade, I was told that he was and that I could do the upgrade telephonically. I thought this was great as they would deliver the phone to me and I would not need to go into the MTN branch. Big mistake!!! In January my son's phone stopped working and I took it into our local MTN branch, they sent it off to their Head Office. In the interim I went overseas for 3 weeks but heard nothing. On my return I had to go to the local office to find out what was going on, they told me that the phone would be replaced as it fell under warranty and I must just contact the MTN number provided and give them a reference number. I proceeded to do this but on contact was told they do not handle this and I must contact another department. I contacted the other department I was told that the local branch was not doing their job and I was to contact them again which I did. They proceeded to tell me that they were doing their job and there was nothing more they could do for me I needed to phone MTN, I tried again and someone tried to help me by advising that they would get the right department to phone me in 3 to 5 working days (bear in mind I was liaising with MTN on this Friday morning from 9:00 to 13:00 and was beyond frustrated). It has now been over 7 working days and I have e-mailed this lady 3 times to no avail and have heard nothing from MTN. My son obviously keeps asking me when he is getting his replacement phone back and I keep telling him that I am trying hard to get it sorted but am receiving no joy from MTN whatsoever. I am very frustrated and do not know what more to do, I have never received such bad service in my life before from any company and at this rate unless something drastic is done will definitely be cancelling my contract for 2 phones and a previous laptop with MTN and moving to another company and will find it very difficult to tell anyone about any good experiences I have had with MTN!!!!!!!