MTN's "Special as upgrade is due!"

I adviced my daugther to go to MTN Cresta and now she has to pay more than R1000 for the "special" they offred her: My previous contract price was R899 per month. I went to MTN in December 2021 to downgrade my contract to that without a device as MTN sent me a notification that an upgrade was due. The price of the new contract special is R599 per month. I discussed this with Cresta branch and I was lead to believe that I would be charged R599 for the next billing. I received and a bill of R 1598.50 which I now had to pay as the next billing! Cresta branch informed today, 4 January 2022 when I went there to enquire, that the old contract only comes to an end in January 2022. Therefore I have to now pay double! The new downgrade price of R599 + the old contract price R999.50 (which is higher than the usual contract price of R899 per month?!). I would have never downgraded if I was informed that I would have to pay double and that my existing contract only ends in January 2022. I was falsely lead to believe that it ended in December 2021. I am very disappointed in the poor service I received, that I was misinformed and **** to. MTN Billing account number: BA***