Did you add them online, or by calling up? Changes made by phone are usually immediate, but online ones can take an extra couple of days to be manually keyed.
Also check the SD Sky Sports channels in 511 > 520. You need to have the (chargeable) HD supplement to access Sky Sports HD in 501 > 510.
If you're still missing them, try following Home > Help & Settings > Help > TV Care > I'm missing some channels.
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