Account in areas due to vodacom refusing to update my billing date

I have a contract with vodacom for 50GB for R320, my billing date was on the 25th of every month. I got a jew job in February and I have been calling in countless times to update my billing date as it moved to the 30th of each month. My account is now in arrears of R742 because my debit order keeps bouncing on the 25th then I manually pay on my pay date. I called in again yesterday as they closed my services and I complained, they didn't help me, they said I still have to pay the arrears, I asked for them to pull up all of my recored calls for when I was constantly calling in to change my debit order, they said a manager would call me and I am still waiting. The arrears should be removed because as a customer I did my part with updating my payment dates and they have failed countlessly to update them leading me to arrears that I have to pay!! It's so ridiculous. My phone number is *** and my email is ***