Does this happen everywhere or in one place @Kate21 ?
As a process of elimination can you try your sim card in another phone and another sim card in your phone.
A Samsung Experience Store or Samsung Service Centre can run a diagnostic test on the phone.
Usually at home. Never had a problem with a y of the other note phones I've had. Also if someone calls me , very often goes straight to voicemail without ringing. Useless !!!
With the issue being usually in your home area that could point to your local network masts.
Check to see if your network has a network checker page online and check if your area is affected.
In regards to your incoming calls and voicemails this is driven by your network. This usually can be lengthened to how many rings before the call goes to voicemail via shortcodes provided by your network. Again if they do this then the procedure will be on their support pages.