Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, a little more background info please:
Appreciate the additional information.
Can outgoing calls be made?
When there is an incoming call, is the ringer indicator flashing rapidly ? ...even if not audibly ringing.
Can you please try calling your home phone number using a cellphone.
Note if Verizon's VoiceMail would answer thus intercepting incoming calls even before these reaches the Panasonic.
Alternatively, please listen if the call would be routed to another number or elsewhere as a call forwarding feature.
Please post back results / observations of the above once tried.
Have you opted / enabled for Verizon's VoiceMail rather than the Panasonic's built-in answering system?
Sorry, I meant before this issue; which is used if you are not able to answer the phone? ...the Panasonic's built-in answering system? ...or Verizon's VoiceMail service?
And based on these tests, it would appear to be a Verizon issue rather than a Panasonic. It would seem that the incoming callas are not pushed through to your home from Verizon.
Have you brought this to their attention ?
The handset has a ringer indicator that should flash when there is an incoming call even if no actual/audible ringing. However, based on "...Nothing happens to indicate incoming calls, not registering info on handsetp...", then I am inclined to suspect that there is no incoming line/signal from Verizon to your home.
Still, yes; the ringer volume can be programmed. Please click HERE.
Which then reenforces the suspicion that this is a Verizon concern rather than a setting/configuration with the Panasonic.
I realize that the above information may perhaps be not what was expected. Unfortunately, there is no quick-n-easy fix and neither is there a workaround doable at the Panasonic's end; sorry for having to be the bearer of bad news.
Still, good luck and thank you too for the opportunity to share the information.