Mis-selling of products and services

I took up a contract with MTN in May 2018 which was two P Smart cellphones for one price which was R400. MTN was never good to me with their services, I would call every freaken month to quiry about the suspension of my mobiles but I didn't make a fuss over that then this year on the 7th of January 2020 which is last month I made an upgrade with MTN and I was assisted my a lady named Happy from MTN Protea Glen mall. And I vividly remember asking her how the upgrade works since on previous contract I was paying for two phones and now am upgrading to one phone and she answered that the one phone from the previous contract would be cancelled from the contract and I will be paying for the new one and only that one. I then asked that if the other phone is being cancelled won't it be affected and she said not at all... And I remember even asking that I will only pay R500 as from January and she said yes but to my surprise the phone that was "supposedly" cancelled from the contract has been suspended and has a total due amount of R600 which I don't know about because to my knowledge that was cancelled and was no longer part of my contract.... So I need urgent assistance regarding MTN Protea Glen Consultant who had missold me a product had she been honest with me from the beginning I wouldn't have taken the upgrade option until I finished the old contract.... Am very angry about this situation and I don't know how will this matter be resolved but I know am not gonna pay for something I was advised that is cancelled. Bad services if this is how MTN consultants achieve their sales target it is indeed a bad habit.... Its a disgrace.