Vodacom's Suspect Invoicing and Incorrect Debit Orders

Extremely annoyed that I am STILL having issues with Vodacom Invoices since last year! I have been charged a double handset fee which has come off my account every month as a debit order and when I had picked up on this, I went into the store to query this.

An item was logged for the double handset fee to be removed and for my account to be credited. Now that I have been "credited" with all the money I have previously paid for nothing - I now "apparently" owe Vodacom R3980?! That is more than half of what my contract actually costs and this is a credit that has helped solve my problem?!

I have also never paid the same amount for my FIXED contract for more than 2 months and then the debit order amount changes?!

The landline constantly just rings and rings and can't get through to anyone via email either - in what world is it okay to just debit people's bank accounts for that it says on an Invoice - but who is checking the invoices?!