Do not disturb not working in iOS 7

I have an Iphone 4. It doesn't seem to have an upgrade to iphone 8 available. Itunes says it is upgraded to the latest version in 7. It has never been "jailbroken."

For the past month some early morning phone calls have woken me up when the Do Not Disturb Scheduled feature is definitely ON. Not all calls ring through. This has not been a problem since early in 2014. I'm not sure if I did anything specific to stop the problem at that time, like a reset. I did do a reset last night and was woken early this morning. Not all calls ring through.

When this first started happening a month or so ago Manual was OFF, Scheduled was ON.

Lately both Manual and Scheduled have been ON, this did not fix the problem.

These are NOT repeated calls or Favorites (I have the feature set to not let repeated calls through anyway.)

Phone is plugged in at night. Some apps (Like calendar and Address book) were still open in the background, but nothing running visibly on the screen.

I have powered the phone off and on using the reset instructions posted by Apple at Turn your iOS device off and on (restart) and reset

and again by holding both the Sleep/Wake button at the top at the same time as the round button to no avail.

Is this still an Apple bug, or is there something further I can do with my current phone?