Does not give what they promise

I took out a contract with Cell C in November last year, it was supposed to come bundled with an extra gig of data, but this never happened, after many calls emails etc with the person that signed me up, they loaded the gig, and promised a credit note would pass each month to the value of the gig, and with regards to the past payments, that was just my loss, but they would give me a 50gig sim to cover that (I dont need this as I have uncapped internet). So currently I have been forced to over pay R1639 and it grows each month by R149.

The call center has also not been able to help me and I am at my wits end.