First, are you sure you have Mix package and not Mixit? I only ask because Mix is quite an old bundle, no longer sold - and Mixit doesn't include these channels. You can check the "channels in which package" guide at the bottom of this page
Second up - when you say you "can't get" these channels, what happens when you try to? Are they greyed out in the guide? Or are you getting an error code/message when you try to watch them.
If they're greyed out and you have a TiVo/V6 box, then try following Home > Help & Settings > Help > TV Care > I'm missing some channels. This self-service refresh takes perhaps 20-30minutes to complete and makes sure your channel selection matches your package.
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