Unfair billing=poor credit

I took out a loan with real people in 2012,I know I paid it off a long time ago...but today I tried to get my credit report and it says I am in arrers. I know the company has close down having paid off my loan I'm left wondering why or how I owe them? I am disappointed but more than worry I know this will ruin my credit because I don't know how or where to contact them, I have tried on several occasions to call and email them without success...Can anyone whose dealt with them help me get hold of them or addresses to any of their offices...I am willing to go to court over this matter seeing as Im left at my wits end.