Help with incorrect tax info from the IRS

I received a letter from the IRS, saying I owe taxes from 2005. It lists w2 info submitted by my employer, however there are 2 different listings on the report from the same employer totaling twice what I would have made in that year. It is clearly the previous year’s info somehow being included in the 2005 report as well. Being young broke and stupid in those times, I didn’t file tax returns, figuring what’s the point, they take my taxes out of my check already. Of course, the employer is a giant company who doesn’t keep records past 5 years. I don’t have the records either.
I’m looking for advice where to start. The IRS says I owe $6000 including fines and interest from that year, when it should be 0.

You should start by calling the IRS, if there’s a number on the letter they sent. I’ve had to call them several times and they are quite pleasant to deal with.