I'm not completely sure what kind of "ancient polytheistic religions" you're looking for, but doesn't Hinduism qualify as ancient and polytheistic?

Shinto in Japan may also be said to be another example, although Japan also did practice Buddhism alongside it.

There are also neo-pagans in the Scandinavian countries who worship the old Norse gods of their ancestors. But of course, this is probably not really a case of the Old Norse religion's continued survival into the present day.

Zoroastrianism is one of the world's oldest religions, although it's not polytheistic.