unable to get free over the air channels

I have an Xfinity internet package which should come with free over-the-air TV. However, I have been unable to get live over-the-air (free) TV channels- CBS, NBC, FOX, ABC, PBS, etc. The same 12-13 channels available free. I tried to contact Xfinity for help but got no help from the autodialler or from the XFINITY chat. What do I need to get my free over the air channels?