Iran is a country in Western Asia.
Iranians have always called their country as Iran. Persia is a province in south of Iran but in the English language the whole country of Iran was used to be called Persia untill 1935 when Reza Shah Pahlavi, the then king of Iran asked the West to use the native name of the country also in the Western languages.
The native name of the Persian language is فارسی (transcribed as Fārsī) (compare with German/Deutsch). Using the name Farsi instead of English in an English text is as wrong as using such sentences as "I speak Deutsch" or "I am learning Italiano".