Defamation of character?

I used to be employed at a casino in west viringa about 6 years ago. I put a 2 weeks notice and quit on good terms due to relocating to college. Recently I just tried to get hired there again, and they said they could not hire me due to failing a drug test and job abandonment. I have never taken a drug test there and left on good terms, So I started to ask the human resources employee if they had the right ss# and everything and she came back and said"awww we had 2 employees with the same name working there at the same time and she must have mixed up our files. I have had a really hard time obtaining employment because of this matter...anything I should do legally????