You might just have to move the antenna around or you might be out of range of that channel. A cable company can't block over the air channels except for through their tv service.
I was on a flight on a Sunday this year and was expecting to catch either a CBS or FOX game because we had the DISH feed on the plane. EVERY other channel worked except those two networks were blocked out. Why? Because these rich cocksuckers haven't figured out how they can squeeze more money out of you so they just blacked out the games.
God I hate the NFL/cable companies. Steal from them whenever you can.