I disputed a listing by Asset Acceptance

Early this year I disputed a listing by this company on my credit file for a cell phone that I do not believe is mine. Per the verification (whatever that is) it was stated as verified. I then wrote a letter to asset acceptance asking for a copy of the signed contract for this collection account. I instead got a bill on their letterhead with Sprint PCS and an account number on it. I wrote them back and sent it certified mail only to get the same thing in response to my letter again asking for a signed contract for validation. At the same time of this letter I had also sent a copy to the credit bureaus with copies of their response to their letter. I still have not heard back from the bureaus. I am at a loss as to what to do, other than changing my font size on the sentence requesting a copy of the signed contract. Any one have any ideas. My letter plainly quotes the fair debt collections and requests them to remove it from my credit file. I simply get a bill and that they have informed the credit bureau that it is disputed.