I can't receive any calls. they all go to the voice mail even though do not disturb isn't on

Other things to check:

The ring/silent switch on the left side of the phone: How to put your iPhone on vibrate, ring, or silent mode - Apple Support

If the calls are from unknown callers, check Silence Unknown Callers: Detect and block spam phone calls - Apple Support

I have same issue and silence unknown callers is not turned on. I also have my ringer set to vibrate on ring, as well as to announce all calls. Most of my calls are going to VM even though caller is on my contact list.