visual voicemail or not

Today I found 7 unheard voice messages left on my Iphone- 11 from two weeks ago. Does having Cellular Data switched off cause messages to hide somewhere? I did not change to it

" The call voicemail" feature manually. Only by switching setting to 'Cellular Data ON' I found the unheard messages, showing up as green dots next to a number. What settings should I set to to have easier view of voice mail messages ? and Can this be done by switching Cellular Data to OFF? Thank you