I had this same thing happen to me this week. I created a schedule for a 3-hour window to send all calls to Voicemail. It worked, but never turned off, even when I deleted the scheduled task. I can confirm that it didn't turn off when it was supposed to.

I can also tell you (because of the helpful Voipo Support staff) that if you go to the "Features" tab, on that main page it has a setting called "Do No Disturb". This is changed to "Voicemail" or "Busy" when you setup a schedule. I tested this by creating a new schedule, and then deleting it. Creating the schedule did cause this DND setting to change, but once I deleted the schedule, it did not change the DND setting back to "Disabled".

This may help some who are as confused as I was about this.

edit: I just noticed that voipinit mentioned turning off DND in "Features". Sorry for the duplicate info.