Worst service ever

I had a contract that ended last year,i was paying over R659 and the phone was lost,in june this year(2021)i called mtn customer service to cancel my contract and i spoke to the lady by the name of Thandi Mthimunye,she convinced me to do an upgrade that was going to work out cheaper than what I was paying,she also promised to courier the sim card to me,the contract was for R129 for 20G data which I thought was reasonable,mtn still deducted the R659 even after the upgrade,i called them and i was told tat the courier guys cant get hold of me,i gave them my number and nothing happened,when i call mtn im being send from pillar to post,this thing is now with their collection department,when i call them im told that the upgrade was canceled on the same day it was done .wow,my thinking is that the lady canceled a wrong contract but i have to pay.im not happy with the way mtn south Africa is handling this issue,