Contract upgrade

19 August 2023 I was contacted for an upgrade on my MTN SIM cards. The lady informed me of my new monthly installment of R358 for both some cards for 30gb each. Asked her numerous times if that is all I will be paying and each time she confirmed the amount to R358 being R179x2. I recently received a statement quoting that the amount due this month is R635.14. I spent 2 hours on a call with MTN and Mondi and the lady told me there is nothing she can do, it is standard to be charged a pro rata. Had I been informed of that, I would have kept my current product knowing that I can't this amount. This is now going to have a negative impact on my credit score because I cannot afford to pay this amount and it's reflecting as a missed payment