Black Friday deal not honoured

I have been billed the normal price, instead of the Black Friday discounted price, for 2 x 30GB contracts bought on the 2017 Black Friday Special. The matter remains unresolved despite numerous attempts since May 2019 to do so. Vodacom Reference numbers given are: EC-1R4Z-207018, INC***, INC***. The Node-to Node department was emailed on 30/7/2019. No reply has been received to this email to date. Phone calls to the same department were not answered. Finally contact was made telephonically with the Node-to-Node department on 6 Aug 2019. The gentlemen advised that this would be referred to their back office for assistance. To date no assistance has been given. I have been overcharged by a substantial amount and Vodacom appears to have no desire to rectify this. I am extremely disappointed and angry.