VODACOM BILLING ISSUE

I had purchased a 2GB 24 month contract from Vodacom with cell number ***. I asked Vodacom to put a call limit of R50 per month on this contract to avoid a huge account. An average of R200 per month was deducted from my bank account for 22 months. In April 2015 an amount of R1593,09 was deducted from my account. I locked a complain on 2015-05-05 ref no ***. Vodacom told me that they look into this matter and come back to me within 7 - 14 working days. I received no responce from them. I send them a e mail this morning and they responded that the call limit service is not guaranteed. Why does they give us the option of a call limit if the call limit is not gauranteed? They also told me that I must settle the outstanding amount and that my account is now with Vodacom's pre-legal division. This is impossible because their is no ammount outstanding because the outstanding ammount was deducted from my bank account. I aslo cancelled the contract because the 24 months was over.