MIL had a similar problem with her box (not a Sky box), but when I did a full system re-scan, I found BBC News 24 had appeared way down at channel 1104 on her listings. I assume they have changed something in the way it is broadcast for logistical reasons and most boxes are clever enough to re-find the channels without prompting. So, all I can suggest is that you find the rescan menu and try from the beginning
Good luck

J