TV service through Cable Card on TiVo has stopped working

All channels display a black screen with the message: "This channel is not authorized. Contact your cable provider for more information V58)". My service is through cable card in my TiVo. I have called Xfinity support and rebooted the TiVo multiple times with no luck in restoring my TV service. How can I get support from an Xfinity staffer that has knowledge of TiVo and the CableCards ? I