Thanks for all your help, I figured it out in the end, as I said I am a novice so all help is very gratefully received.

In the main day menu I deleted the existing options and pointed option 1 to the new sub-menu that I had created for company A (rather than an extension as it had previously been set to), then I repeated the process for option 2 to sub-menu for company B. To allow the caller to repeat the menu options I again just set the relevant key press on both sub-menus to point back to the sub-menus I had created.