I saw you edited your post. Please note that the forum software does not notify parties that an existing post was edited, as in, I would've never seen your response if I did not open the thread and scroll up...
In context of the OP, my interpretation of the situation is that the OP took out a contact in 2016. Sometime after 2018, when the contract was in its month to month state a 3rd party, not authorized by the OP, upgraded the contact - fraudulently.
This is my assumption. @winner Mind clearing that up please?
Lets say the upgrade happened in 2019. The OP then disputed the upgrade and Vodacom correctly cancelled the upgrade. Now Vodacom is refusing to cancel the underlying 2016 ""contract"", as, according to them at least, one can only do that at the end of the new contract period, at say e.g. the end of 2020. The 2016 contract should be in a month to month state, and the OP should be able to cancel it with e.g. 1 month notice.