Of course races exist. People who say they don't don't understand either biology or sociology. What you're trying to say is that in humans, race is primarily a cultural and sociological concept rather than a biological one. Races, as commonly defined in human society, are not biologically meaningful.
Biologically meaningful groupings within the human species DO exist. There is no one catch-all term to describe them, because they are defined in context. But we might talk about the Icelandic population or the Han Chinese ethnicity, or so forth. Population is a fairly common word for it, but it can also be used to describe other concepts.