False Adverti*****t

I signed up an additional contract with MTN for a Samsung Galaxy S6 Edge Plus and the price for it is R599.00 per month. I checked my invoice and they are charging me +R721. I called them more than 10 times to have this rectified and I was promised that it was going to be amended. Up to this day it is still not sorted. And their Customer Care Agents are useless and clueless. I gave them a copy of my agreement and it looks like no 1 at MTN wants to take responsibility and sort out the billing error. I want this sorted out urgently!