Incorrect billing (Overcharged)

In August 2019 Telkom was running a special for a wifi router priced R250 per month 20 gig. from September 2019 till now Telkom has been billing me an amount of R757,55 monthly. I have called Telkom several times and they agreed to sort out the incorrect billing but there is still no change on the matter. I do not wish to cancel my deal but I just need this matter resolved as when I subscribed on this deal I only budgeted R250, nothing more. My reference number for the last call to Telkom is ***