********** refusal to cancel contracts

I expressly called vodacom to cancel my contract for two phones . The service consultant advised me to keep one on a much cheaper price and to cancel the one I’m no longer using. They agreed to this and when my invoice came they only upgraded one and left the other one running which has caused arrears. I called them for a resolution but they now only mention to have heard only the part where I took their new offer and they mysteriously ignore the concern about the one I requested to have cancelled on Twitter. This level of unprofessionalism and ***** cannot be allowed