Wooworths and thier pathetic revolving loan structure.

I have had a long standing revolving load with woolworths which has been ok apart from a few miss haps (such as them continuing to debit my bank account after paying up the loan at one point.) this was up until my most recent withdrawl. I was advised that there was "x" amount available to withdraw, i withdrew the amount and was notified via sms of my monthly amount that I was liable to pay for this. the end of April rolled on and my debot order ran off charging my almost R1000 extra. I contacted woolworths as this was not the amount i agreed to and refuse to pay so much extra without notice or warning. I was told that it was due to thier books not calculating the interest correctly, which if you ask me is not a customer problem but a woolworths problem. they apologized for this error and advised they would refund the difference that was charged within 7 days. 2 weeks later I still had not received the refund, I called back only to be told they were awaiting a bank statement from me in order to process the refund. this was very surprising as they never needed the statement before to take my money but needed it to refund the money. they soon realized this was aagin a error on thier side and that had i not called in the refund would never have happened as woolworths again dropped the ball with no one reaching out to me to advise why the refund is being held up. a manager took over the call and authorized the refund, he also assured me this would not happen again and assured me that he would send me something in writing to confirm this, surprise , surprise no writing confirmation ever came. Last week I received my statement and to my surprise, again i am being over charged again, I called in at the time and again spoke to a manager who confirmed the debit order would be cancelled as there was still time and the correct amount put forward for the debit as the error was on woolworths side. He also assured me I would receive confirmation in writing, again no confirmation. This morning I received a sms notifying me of the wrong amount to be debited off my account. I called and was told by some muppet that the solution is to tell my bank to dishonor the payment, he advised this would not impact my credit score and that the amount he advised me to pay was also incorrect and short. as it stands they say there is nothing that can be done and the only fix is to not pay?????? How can this possibly be the solution to a problem created by the financial institute. This also means that what I was told last week never happened and I was **** to by the "manager" that I spoke to. I am now having to pay extra on the loan as woolworths can not calculate interest correctly and expect their customers to pay the shortfall with absolutely no warning of this what so ever, not even a sms to advise. I have also been advised by someone in the contact center that their application and information given on there is not correct and we should not use that in future, I would like the extra funds that i am being charged to be refunded back to me if possible!!!!!