verb
BAD : She told the shop assistant that she wanted to protest about the cardigan she had bought.
GOOD : She told the shop assistant that she wanted to complain about the cardigan she had bought.
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protest = say or do something to show that you strongly disagree with something: 'The crowds were protesting against the government's purchase of nuclear weapons.'
complain = say that you are annoyed or unhappy about something: 'He's always complaining about the weather.' 'If you think you've been overcharged, you should complain to the manager.'