Phony upgrade, ******* charge for non existent devices

To add to my complaint yesterday, I was called by someone identifying themselves as MTN upgrades department in November 2017, went through a telephonic upgrade process, phone never arrived so I naturally assumed it just didn't happen as I had no number to call, no ref for the upgrade.... nothing!!!, and now see they "did it" and have been charging me for a new handset that has never been delivered. And they say I must find out what went wrong - call centre says its not their responsibility to drive my complaint?????? Not only that, my old contract finished 6 months prior to the so called upgrade - therefore my contract handset now belonged to me ... but they still took money off for it every month along with the subs even though I owned it after 2 years contract was up... and you cannot get to speak to any one other than call centre agents.... no managers or decision ,makers or resolvers. I am just so disillusioned and have nowhere to go to get this fixed and get my money back or my contract restored to it's original. Further My tablet contact also reached it's renewal at the same time and I see I am still being charged for that device too????? What do I do to stop them *******ly charging for stuff I own. So now I am being *******ly charged for 3 separate issues. Their call centre says I have been upgraded and insist I have been sent devices and therefore WILL be charged!!