In arrears with an unknown account

In 2014 I took a loan with FNB then I got retrenched at work and I couldn't pay the loan anymore...then when I got the job this year I went to FNB for arrangements and asked for settlement amount then I paid it cause my account was already sent to collection,I paid it finish in August then in November I got a paid up letter but funny enough on my credit report it shows 2 accounts,1 was closed in October then the other says i'm in arrears but I only know 1 account...which door can I knock on at FNB so that I can be helped with this regard cause no one wants to give me a car finance because FNB says I am owing them n I am in arrears...can anyone from FNB help me please