phantom phone billed to account

Hi,

We've been with AT&T for several years and have 1 landline on our account.  Today I noticed that I have overlooked a charge for a phone to our account for QUITE a while for a phone number we don't have, so I called att and spoke with a rep. who opened a claim for me.

What's bad/disconcerting/strange about all of this is I immediately called this unknown number after discovering it on our bill from our home phone (serviced by att) and it patched me through to what sounded like att customer service.  I then called this unknown number from my cell, and it went to a generic voicemail both times I tried.  The rep at att took the line off of our bill and after I got off the phone with her, I again called the unknown number and it then gave me a recording saying that the phone number had been changed and there was no new available phone number.  I find this all very suspect and was giving a billing cycle to have them resolve this.  I am looking to be compensated completely and I'm wondering if anyone has had a similar experience.  It does seem like others have had this happen, but have several phones or devices.    Someone suggested in another thread, following up with a fraud complaint, which probably will be my next step.  

Thanks.