Vodacom's ********* behaviour

I received a call in September from a salesperson from Vodacom. The call was recorded. They offered me an additional 100minutes and 1 Gig of data for only R20 more. I specifically asked them to confirm that I will only pay R20 more. They confirmed and I accept the offer. Around the 1st of October I learned (on my app) that they are now charging me about R200 more. I called and asked them to reverse the "so-called upgrade" as I did not agree to it. The lady logged a Call/Serviced Request to do just that. I have not heard from them again, but my app is still showing the increased amount that I owe them. I have not attempted to contact them again as it is too frustrating to try and get hold of someone that can assist. I will seriously consider cancelling Vodacom al together, fibre contract as well.