Vodacom Billing ****

I have a Flexi Top Up Contract - Reason for it and this is also what I was sold is that there is no surprise billing - You have a fixed monthly account and adding data or airtime is a cash transaction. With flexi you can choose to split Data and airtime so when I chose to split my data and airtime I select the option to recur monthly. In Vodacom's world it means that from next month on it will not recur the transaction like you requested but they will bill you an additional amount for this transaction. I consider myself educated and tech savvy but this does not add up. Firstly this means that your topup contract is not a fixed billing anymore as you can add to the bill - Even unknowingly so - PLEASE explain Vodacom how a fixed bill contract can be manipulated to increase its billing amount.