I have charter. Same problem, couldn't fix it with tv remote, had to use the charter remote.
- Leave tv on, press cable button on remote and then power, this shuts off cable box.
- Press menu key
- First line showed 4.3 setting, I changed it to 16.9
- Second line showed HDMI cable at 480, I changed it to 1080.
- Hit power button again, this should turn the tv back on.
- Fixed my problem.
- I think you also can call charter and tgey can help walk you through it.
I didn't even know about the settings on my charter box until researching on the internet. I contacted insignia, they told me by using the cable box it overrides the tv settings.
Hope this helps