Vodacom's empty promises

After many conversations with Vodacom and their empty promises that they would stop charging me monthly R480.00 instead of R299.00. Furthermore, they are obligating me to a two-year contract which I never agreed to. This can easily be checked through our recorded conversations. On 7th May, during our last conversation, they promised to investigate the matter and call me back within 24 hours (Reference number: ***), but nobody has contacted me to date (12th May). However, I did receive a new invoice for the next payment of R480.00.