Comcast Digital Cable, The Case of the Swapped Channels

My family has recently gotten the comcast digital cable, which includes On Demand (no DVR). Today, it started having an issue with which channels are which. For example: We tried going to channel 56 for CNN, but instead got some tv show on channel 13. The info that goes with the channel has been correct with what the channel should be (like CNN), but still will give us the actual picture plus audio (like a normal show) of the show that has replaced the true show. This has occurred on and off all day and has had us baffled as to why it has been happening. We have no idea how to fix it. Besides this problem, everything else has been working just great.