Accounts in dissarray

My debit order bounced in June and my subscription did not come off. I called them to make an arrangement that said they could deduct double at the end of July which I assumed they had done because the amount they took off was more than my installment. End of August I didn't have money to pay them again and thought I could make the same arrangement, it turns out they didn't do as I had asked and I now owe them more. They are demanding that I pay or they will suspend my services. I know I am in the wrong by not paying them but who's fault is it that they did not take all their money?? I am really so angry!!!!!