A lot of these on the forum. Check Help & Settings / Settings / Entitlement Information in the Vision box munu. There should be a list of channels you are able to view. My guess is that the BT Sports channels arn't listed. Could you confirm what is actually showing.
Ah looking at your post again you say you can't see channels 507 to 512. Does that maen they arn't there? In that case you need to check:
Help & Settings > Settings > System Information > Middleware Version
You should see something like:
4.79.5 rev.1 512-multicast Build 312754 Jun 4...
If the "multicast" isn't showing your box needs updating to the multicast software.
The box is supplied with non multicast software and the multicast is downloaded when the system realises you need it. This may happen overnight tonight, so make sure and leave your box on. If it doesn't you'll have to get in touch with support to make sure it gets downloaded for you.