New Installation Cancelled

I recently signed up for cable/internet to be installed at my house that I've owned now for over 2 yrs.  I have never had AT&T service before.  After my first order being cancelled, I signed up again online and went all the way through the process.  My scheduled installation date was tomorrow afternoon, so I already took vacation time to be there for the installation.  A few hours ago, I received a call saying that my order had yet again been cancelled and wanted to know if I wanted help processing a new order.  After speaking with a supervisor, I found out that there was an active account at my address (although the service has been turned off) from a previous owner (I assume) and I could not proceed w/ having service installed until that account was officially cancelled.  The supervisor on the phone told me that I needed to track down the pervious owner of the home.  After explaining that I didn't know the previous owner, she told me that my realtor would know their name and I should contact them.  My realtor was a personal friend of the family who no longer is in the business.  Why would it be my responsibility to track down this old customer for them???  If there is an outstanding balance, that is AT&T's problem not mine.  Since I work in Finance, I know that if there was an outstanding balance with the account it would have already been written off at this point.  Why would they turn down new business just because they have an outstanding issue with a completely different customer?  What can I do to get service???