barking up the wrong tree; calling at the wrong house
Used when someone's approach, target, or assumption is mistaken; often appears in the set phrase お門違い (o-kadochigai) with the honorific prefix.
See also: お門違い
Complaining to him is barking up the wrong tree.
That complaint is for the wrong department; you're calling at the wrong house.
barking up the wrong tree; misdirected effort or complaint
Compound of 門 (kado, 'gate') and 違い (chigai, 'difference, mistake'), literally 'wrong gate'. The exact historical derivation is uncertain, but the phrase likely originated from the idea of mistakenly arriving at the wrong entrance.