Bad service, Overcharging

I took out a 24 month R299.00 mobile data modem contract on the 14/10/2016, which expires in Oct 2018. I called in on the 31/08/2018 to give Vodacom notice of cancellation. My normal monthly billing (debit) is R301.62. At the end of Sept 2018 I was billed R490.48, which I queried and was escalated, with no response after the escalation. At the end of Oct 2018 I was billed again R490.48. I called in and the consultant said I am billed without the promotional discount because I didn't cancel the contract before the upgrade period of 22 months. When I was doing the cancellation this was not told to me and even so the contract app**** for was for R299.00 over 24months and not R299.00 over 22months. Vodacom is now owing me R377.72. ****************.