CALLS GO STRAIGHT TO VOICEMAIL

When your iPhone is locked (the screen is off), Do Not Disturb silences all incoming calls, text message notifications, and alerts on your iPhone. Unlike silent mode, Do Not Disturb sends incoming calls straight to voicemail.
https://www.payetteforward.com/why-does-my-iphone-go-straight-to-voicemail-heres-the-fix/

https://forums.androidcentral.com/verizon-galaxy-note-2/306427-all-calls-going-straight-voicemail.html

go to contacts in the phone, go to your entry, press sub menu button, uncheck incoming calls (send calls directly to voicemail)

dial #002# send, then ##21# send. that should cancel all forwarding.

You need to contact your service provider and have your Voicemail reset. The carrier can reset everything. This includes fixing your incoming text problem.

check your incoming calls settings and see that you did not choose it to divert to voice mail number

Sorry to hear you are having issues with incoming calls. You do wanna try a few tests. Check to make sre there's signal on your phone. There are no coverage issues. Do a powercycle, by powering the device down for about 10-30 seconds. If you have another phone with the same carrier, put your simcard in that phone. Do a test call. If it goes thru, it's software issue. If it fails, and goes straight to voicemail, then it's a network issue. Contact your carrier ASAP to get it resolved. If it's happens to be the phone. View the manual how to set the call forwarding. If that is set to be ringing and not straight to voicemail. Try a soft ware reset aka Master Reset. Your manual of this particular phone will be in there. You won't lose our number, pictures, message, etc. You'll see the phone will have the original ringtone and wall paper as if you just got it out of the box.

Cheers!

check in settings/phone to see if you have maybe turned on call forwarding and it is being forwarded automatic to your voicemail box number

i would got into your voicemail settings and check to see if you have it set to ring once then straight to vmail.. i'm not sure how your phone is set up completely but i would assume you can adjust the amount of rings before vmail picks up.. is this phone new to you?
hope this helps..
d