Data Charges and mistake on carrying data over not happening

i am having a horror of a time with Vodacom, i renewed my contract last month, and i finally got what i wanted, which was more data, and now the data does not get carried over, and i provided proof to the lady, so she seen the mistake and for some reason could not get it carried over or log a request for it, so she assigned me 2 GB's data in the interim, but now i see it on my bill as 2GB, but i refuse to pay for it, as that is their mistake and it needs to be removed asap, but my data needs to stay as they owe that to me, and this needs to be every month where my data gets carried over.