Incorrect calculations on statements

Where do I even begin to describe my frustration with this useless institution.

Every month I make EFT payments to my vehicle loan account at Absa seeing as they stopped debiting my account for some reason. I have also noticed that my statements reflect the payments however my arrears amount increases every month and sometimes with even more than what my Installment is (sometimes double and even Triple). The amount that is showing as outstanding is impossible as it's almost as much as all the installments so far. This is also affecting my credit score very negatively. If this is not resolved, I will be contacting my lawyers.