Private College Student Loan

What can I do to straighten out a mistake a student loan company made? A student loan company has been sending me invoices for a few months now. The problem is that the person they are referring to has the same name as I do with the exception of the middle name. His middle initial is "L", but I don't have a middle name. They called me a while back and I told them the problem. When asked if my SS# was such and such, I said no. They then asked me if I attended the University of Oregon, I think it was. I said no and gave them the name of the college I attended. They then said, "Oh, ok." and hung up. I figured the matter had been settled and they realized they had the wrong person. What I'm guessing happened is that this other person with the same name as myself was listed under my contact information, and now I'm getting his invoices. I've already begun paying my own loans off as of August. So, I'm all set as far as paying off the debt. However, I am STILL getting the invoices of this other person with the same name as myself. I've cleared this up twice with this loan company and they are still sending me invoices. I recieved another letter from them today saying that "the default of (my) student loan(s) has been reported to the national consumer reporting agencies" and that my "credit rating may have been damaged by the reporting of (my) default". Now, I'm almost positive that they don't have my SS# and instead have this other person's, with my name, instead. I'm thinking that this poor other guy hasn't even recieved any of these invoices and is oblivious that his credit may be damaged. I plan on calling them again tomorrow to clear this up once and for all. My question is, if this third time doesn't straighten the matter out, what else can I do? Also, if it makes any difference, this loan company sending me these invoices is "Northwest Education Loan Association" or NELA. I took my loan out with "American Eduction Services". What I'm wondering is, how did this other loan company confuse my contact/mailing info with someone else's even though I never took a loan out with them? Any help would be greatly appreciated. I've just gotten off of the phone with the company and what had happened was the first two times I'd called, I'd been directed to the wrong department and the mistake was never cleared. This time, however, I was directed to the default loan department and the representative confirmed the mistake by asking me if the last 4 digits of my SS# was so and so and I'd said no. Also, my birthday did not match the one they had on record. She'd told me that what had happened was that my mailing address was mixed up with this other person's via the yellow pages. Anyway, I'm sure the mistake has been settled and I appreciate your all's input :D And I just checked my credit report online and it's perfect.