Credit score negatively impacted even though debit order goes off successfully

This institution has completely ruined my opportunity to buy a house or take out any credit. They reported a problem with their billing system the first month that I needed to pay so I paid manually and thereafter the debit orders have gone off successfully each month. This is not what is reflecting on my credit report and my score took a horrible knock. I have had no response from Courtney and each month my score gets worse. I am on the verge of taking legal action as this loan has caused more issues than the actual surgery.