How do you turn off voice mail

I have 2 reasons for doing so - 1. I'm a professional driver. If you ring me and I don't answer, that'll be because I'm not available to talk. I will call back when I can, but I don't want people to think they can simply leave me a voicemail for something urgent and assume their message has been passed on. If my phone rings more than a couple of times in a row, I will conclude it's urgent and find a safe place to stop and see what's going on...

2. I have a child who is subject to a care order. Aside from also being a bit naive for their age, there are particular people in their life who are related, but with whom, 'access' needs to be controlled due to particular risks they pose. One such individual has no phone contact authorised. Consequently my child's phone is heavily secured using a variety of apps and inbuilt privacy/blocking settings etc. I am concerned that there's a possibility that a person perceived as a risk may be able to leave voicemail for my child and hence wish to disable that functionality.

I get voicemails left from automated calls quite often that's why I don't want voicemail

Because some just don't want have to access it to listen to any, I can see their point most communication is WhatsApp or such like or calls nowadays anyhow tho I have had a robo-call, (automatic voice call) go on soo long they've gone into the voicemail...