The film follows a young Polish woman who is imprisoned by a Sicilian man.
"This should not be anyone's idea of entertainment, nor should it be described as such," said Duffy, who recently revealed she was held captive and raped a decade ago.
Netflix said it would not remove the film, which it said carried warnings.
Adapted from a novel by Polish writer Blanka Lipińska, 365 Days was not produced by Netflix, but was picked up by the streaming service in June after a theatrical run in the UK and Poland in February.
Billed as an "erotic drama", it has quickly become one of the platform's most popular films.
The Guardian recently described it as "the Netflix softcore porn film that people can't stop watching", and The Atlantic said it was "Netflix's first summer hit".
Variety magazine, however, called it "thoroughly terrible" and "politically objectionable".
In a letter to Netflix chief executive, Reed Hastings, Duffy wrote: "It grieves me that Netflix provides a platform for such 'cinema', that eroticises kidnapping and distorts sexual violence and trafficking as a 'sexy' movie.