Set up voicemail on my phone a while ago, then tried changing how many rings before it kicked in which messed it up completely. Current situation on my iPhone 16 ………

When someone phones me, after about 5 rings the caller is told the number you have dialled is not recognised. It is the same whether I enable or disable the voicemail from my id app, or after dialling 123. 
When someone phones me it appears on the iPhone screen and I can successfully press the “voicemail” icon on the screen (instead of waiting for “number not recognised”) and the caller goes to voicemail, but is not greeted with my recorded message from the greeting I recorded from calling 123. Instead it just says call is being forwarded to voicemail. And I get a message saying I have a voicemail message which I can retrieve by calling 123.

What is going on, how to get rid of this “not recognised” for outside calls, how to get my voice mail working?😟

Any help/advice would be appreciated. 😊

Other info …
My number is an idmobile eSIM.

Have tried getting my kids to phone me from their idmobile numbers and they get the number not recognised message. So how can this be?

And I can call them successfully. 
I have no issues sending text messages to them, or receiving text messages from them.

A mystery to me 🧩