Die Person, die die Polizei angerufen hat, war sehr nervös.
Duolingo asked me to translate this sentence, and my answer "The person who the police called was very nervous." was marked wrong, with the correct answer provided being "The person who called the police was very nervous". Shouldn't the relative pronoun die remain the same in either nominative or accusative? Also if I remember correctly die Polizei as a collective noun is singular feminine in German (as opposed to British English where "the police" licenses plural verbs). If that's the case does my interpretation also work?