Deliverately misleading clients

On Fri I contacted MTN to upgrade my data contract as the 24m period ended. I received a call back from a number identified by my caller ID app as 'MTN'. The agent identified herself as an MTN agent and proceeded to assist me with the upgrade and following the conversation I received a contract from MTN indicating the agreed amount of R399 per month. However, I received the debicheck mandate from my bank requesting approval for a monthly payment for R1019. This is clearly not what I agreed to and as a result I emailed MTN immediately indicating I do not accept the upgrade as I am still within the cooling off period. I received the automated reply from MTN. This morning when I called MTN I was informed that the upgrade was done via Rewards Co and I needed to contact them. The call Centre number sate that I am calling outside of business hours which is 8h00 - 17h00 on a Mon - Thurs, even though it is way past 8am. It very clear that the contract includes hidden costs and add-ons that I did not agree to. And at no time was I informed the contact is with a 3rd party and not with MTN directly. I tried addressing this via MTN but they referred me to RewardsCo who I cannot reach.