Interest debit order problem on woolworths side

July August and September my debit order has not been coming off. A problem on woolworths personal loans side yet every time I phone they say I did not have money in the account. Yet every month on the 17th the money is there . I phoned in time and time again telling them there is money in the account take the money they refuse they say they can't and they cannot explain why. I was even told to pay cash in August month which I did and then they took a portion of the debit order as well. In the meanwhile I am being charged interest for the problem on their side. I want my interest reversed and my debit order to work!