Overcharged by Cell C

Cell C is overcharging me with more than 180% on a monthly basis. I canceled my subscription after 24 months and the service agent offered me a deal to remain a Cell C customer. The deal was telephonically confirmed and the audio recording is clear. It's been 26 days since I reported the matter. All they say when I phone is that they just wanted to call me and that they are waiting for another department to provide feedback. Pathetic and poor customer service! Ref numbers *** and ***.