This is what CALD says:
whatsoever (ALSO whatever) used after a negative phrase to add emphasis to the idea that is being expressed:
He has no respect for authority whatsoever.I can honestly say that I have no interest whatsoever in the royal family....
Is whatsoever often used in (1) casual and (2) academic language? Is maybe whatever preferred?
Also, in contemporary Britain, young teenagers use "whatever!" when they want to reply that they are just not interested.
It is particularly annoying, but that's teenagers for you!