Vodacom are being dishonest

Last month I upgraded my contract with Vodacom. According to the lady you I upgraded with, the new catract included a once off 10GB data bundle as well as 2GB x 24 months free of charge. I have not received the full 10GB, instead Vodacom gave me 6GB and I still have not received the 2GB as I have been promised. Then to add insult to injury, Vodacom sent me an invoice of R1 693.00. They were charging me for 12GB I have not recieved for December. They said that the invoice would be corrected, but on the new invoice I am still being charged for both this contract as well as my old contract. Vodacom arr once again *****ing from me!