The only way to force Word to never use Calibri is to uninstall the Calibri font from Windows. This may have unwanted side effects.

If you routinely use the default new blank document, which you shouldn't, you need to edit the Normal.dotm template to use a different font.

If you use your own templates, which you should, simply change them to use your own preferred font.

The simplest way to do this is create your own Office Theme. From the Design tab apply the fonts and colours you want to use then from the Themes menu select Save Current Theme.