Not sure if there's a special place to put discontinued numbers.
However, the Tax Credit office number 01274 894001 listed in the database for use instead of 0845 300 3900 now goes straight through to a recorded announcement asking you to use an 0845 number.
I know there's a link to add new numbers but (if there isn't already one that I haven't spotted) it would be useful to have a link to report numbers that are no longer working or only take you to a recorded announcement.
~Edited by bbb_uk: Edited title to add area.