What was the name of the man who told Columbus he wasn’t in India he was in America?

Amerigo Vespucci

Explanation:

And that was the realization that what he was looking at was not India at all, but an entirely new continent. He verified the fact by following the coast of South America down to within 400 miles of Tierra del Fuego. Columbus found the new world, but Vespucci was the man who recognized that it was a new world.

Christopher Columbus finds Indian as well as America

Amerigo Vespucci