Horrible customer service

I wanted to settle my account with them and was offered a 20% discount then an arrangement was made that my account will be debited with the discounted outstanding amount. A few days later I got an email from them saying I need to make a payment urgently as they were going to take legal action on me. I went into my account to check if the funds never went through and immediately made the payment of the amount specified on the email. again a few days later, I got a call fro one of their consultants who then said I still have a balance on my account. then I relayed the story to her, she then turned around and accused me of no having money in my account on the day. I told her I would take legal action against her for making allegations she cannot back up, she then put the phone down in my ear. For the past month I have been getting numerous calls from different different consultants demanding that i make the payment of the balance in my account and I refuse to make the payment because it wasn't my fault that they did not load the debit order on the day that they said they would and now they are making me pay for their mistake. The issue was then escalated to management but they came back saying that there's nothing they can do. My question is why do they offer discounts only to take them back and charge you more because they failed to meet their end f the bargain.

I am escalating the issue with the Credit Ombud as I refuse to pay for their employee's mistake.