Incorrect upgrade

So Vodacom contacted me and wanted to sell me a contract and i refused and said i am interested in the R199 20 gig deal and told them il only be happy with that deal if i upgrade. Lady first said no then 20minutes she calls me and said it can be done. I check my bill on the app and contacted support and says i will be charged R399 for 20gigs . When i specifically told her i only want that upgrade if its R199. Vodacom sales do not want they doing its either you revers it and get me back on the contract of 3gigs or you upgrade my contract to 20gigs for R199 only.