Translation:To be fired.
Keeping in mind that translation can never have an exact match,
해고되다 is closer to the English expression "Get laid off".
파면되다 is perhaps the equivalent of "Get fired" i.e. get dismissed through one's own misdoings.
Just like in English, there are variants (some slangs) to describe losing one's job. But in common usage, 해고되다 seems to cover most circumstances.
Become works with adjectives but not verbs. Yes many verbs in the past participle are used as adjectives, which can give two slightly ambiguous interpretations. But "fired" is not used as an adjective, only as a verb in this sense. So "be fired" and "get fired" but not "become fired". "Unemployed" is an example of the opposite where "become unemployed" works but "get unemployed does not". Note also that with "be" it forms a passive with verbs like in "to be fired" but with adjective "be" links the adjective to the noun.