DATA OVERCHARGED!RE: Vodacom

On 28/7 I receid a sms to say my data bundle had run out. I topped up my account as I know how expensive data is. I have a app on my iphone to check my billto make sure it doesn't go over between R600 and R800 a month. On that Tuesday I checked my account and it was sitting on R680. The next morning I checked my account again and to my horror my bill was sitting on R2 455.96. I queried the bill, to be told that I used data that was out of the normal rates and when I got the breakdown it said I used 40 minutes and had been charged R1 528.37 for that. How can it cost so much for 40 minutes even though, I know I had bought data that night. When I phoned the help desk again, I got told that yes, it is correct and I did use the data so I must pay! Then I received a letter to say: We reviewed the data usage on your number and after a thorough investigation, it was confirmed that the data usage and the billed amounts are true and correct. But as a valued customer as a once off gesture of goodwill, we are prepared to credit your account for the amount of R765.43 for the data charges reflecting. How can Vodacom charge R1 528.37 for 40 minutes of data? Thank you for 20 years Vodacom!