Contract is 500mb, Autopage charge for 3gb

I've upgraded my contract to a 500mb data top up for R249 per month. 2 weeks ago I received an invoice for 3gb top up, amount R580. I've send an email regarding it to Autopage. I've phoned a week afterwards. Still nothing. And well done, the amount of R580 gets deducted from my account. I only receive 500mbs data per month. The contract shows 500mb per month. But the invoice show 3gb per month. That's contract break from your side and I don't receive any feedback from you