ACCOUNT HANDED OVER IN ERROR

My account was handed over for failure to meet financial commitment, however I was not aware of the amount outstanding as I had instructed Discovery to deduct the amount over a 3 month debit order. Whoever was responsible for processing the debit order did not deduct the first debit order on the agreed upon date and therefore the payment was defaulted and a few months later I got a call from the attorneys who then said my account has been handed over. I then queried this with Discovery who then admitted that the error was from their side and they will close the account with the attorney. I settled the outstanding amount with discovery and forwarded the relevant correspondence to both parties. I then received another phone call from the attorneys a few weeks later stating the amount is still outstanding and I once again sent through the correspondence. I then received another phone call this morning from the attorney stating the amount is still outstanding, I once again have sent through all the correspondence. Either the attorney or Discovery is not attending to my account and I would appreciate feedback!!!!