countable/uncountable a written or spoken statement in which someone says they are not satisfied with somethingmake/file/lodge a complaint: I intend to make a complaint.
complaint about: Customers lodged a formal complaint about the way they were treated.
complaint against: An alarming number of complaints have been filed against him.
complaint that: The council has received complaints that the building is not safe.
investigate a complaint: All complaints are thoroughly investigated.
uphold a complaint (=say it is reasonable): The Commission upheld the complaint under Article 13.
grounds/cause for complaint: If they had a more caring attitude, we’d have less cause for complaint.