how do i change voice mail settings on iPhone7

Disabling voicemail is likely impossible, but if it can be done, it would be your cellular carrier that would do it.

The list of callers appears when tapping the “Voicemail” tab in the Phone app, assuming you’ve set up Visual Voicemail.

Set up Visual Voicemail on your iPhone - Apple Support

You asked how to resolve some issue.

Instead you should tell us what issue you’re trying to resolve.

Voicemail settings is the incorrect approach.

I don’t know what “mob provider” means. If it means cellular carrier, then that sounds correct.

Enjoy your iPhone.