The FAQs appear to be written for the advertiser’s view of the pages, as I can’t see the links they refer to, for checking who sent in your feed.

One thing that may have happened was, there was a glitch on the day you tried to remove this listing. A strange thing to try, which MIGHT work, would be to put this property back into the feed for one day, then removing it the next. This might pick up this orphaned one. Of course it might just come up as a new separate listing, and that disappear te following day.

This is NOT an ordinary ad-removal issue, it is a technical problem with the site, and they should have someone prepared to accept a bug report. So approach it as a bug report, using your listing as evidence, rather than asking them to remove your listing.
References :

You can call 866-562-7219. That number is only for paying customers but that should include you. It is the Customer Service desk.

help.yahoo.com is worth trying. But they don’t answer you very explicitly. So explain your problem as clearly as you did in this question.
References :