You don't need to worry about deb.linuxmce.com since is not used anymore and the new update mechanism doesn't use apt. The new updates are from updates.linuxmce.com and are applied with a custom update application.
First, you should figure out if you are using the last mythtv, should be version '0.20.2-0ubuntu0.7.04~proposed1'. You can find this out by doing a 'aptitude shot mythtv-backend' and look on the 'Version' field.
If you got the right mythtv version that means the update ran ok, so probably what you need to do it make sure you have added your schedule direct info correctly (note: data direct service is not available anymore). Run video wizard and go on the providers page to set this up.
If you checked all that and still have no channels, you can look on schedule direct web page and check that is all ok in there and after that run 'mythfilldatabase' from a console and see if you can spot any errors in there.