Which is correct: 'Gracias por visitando Argentina' or 'Gracias por visitar Argentina'?

I am doing a spanish project, and on the power point, we are supposed to write: 'Gracias por visitando Argentina' I am not Hispanic/Latin, but my step mom and her whole side of the family is either from Colombia or Panama. They say its wrong. It's supposed to be: 'Gracias por visitar Argentina' when i told my teacher, she said that my families way was slangish, and she was right. what do you think?