I would do as @Emiel1 suggests @Kyle411 and use the contact host function on the listing.
Do the previous owners not have an email or phone number for the people they asked to act as hosts for them?
If you have a link to the listing it should tell you who is listed as the host on the listing which if they are a management company will help locate them. At the end of the day you cannot ask them to take down the listing as you were not the person that contracted with them to provide a management service, so they will need to contact the original owners for confirmation.
It seems strange there were never any bookings. Are you sure the listing is still live?
If you want to host on Airbnb just set up your own listing.