Having an item removed from my credit report.?

I will try to make this as short as possible. I had an ex who obtained an apartment in his brother's name (this was found out after I moved from Pennsylvania and talked to his family) for us because I wanted to move from PA to CA. So I moved in and two weeks later an eviction notice was taped to the door. I asked him what it was about and he said his dad will take care of it. So I take the notice to the office and they said the money orders that were given to them to pay for the 1st months rent and security deposit were fraudulent. So I moved out and a couple years later I check my credit report (I never signed a lease) and this $5,500 debt is on my report. I can only guess that he had someone use my ID and sign my name on the lease. So I sent the company a letter through certified mail and gave them 30 days to respond and they haven't. The item still remains. WHAT'S THE NEXT STEP????? I CAN'T SEEM TO GET THIS DEBT REMOVED, ANY SUGGESTIONS ABOUT WHAT I SHOULD DO?