Permanently disable the option of voicemails from callers

Hi, I have an iPhone 18.6.2.

I don't want anyone to have the option to leave me a voicemail when they call my phone.

(Please note, this is not the same as blocking certain callers, I know how to do that and it's not the same as the query I am posing here. Neither do I want to forward calls elsewhere).

Have followed tips online to disable, but nothing works.

The option of "Live Voicemail", on my iPhone, whereby you can allow or disable voicemails, does not appear as an option on my phone for selection.

I deselected "Notifications" as per another online suggestion, but that does not work.

I understand that my network provider generally needs to get involved, so I entered *#004# into my keypad (from more online advice), quite a lot of text appeared on the screen and frankly I could not decide what to select - have attached a screen shot.

I asked somebody to ring my phone and sure enough it went to voicemail.

Any ideas or advice?

Many thanks