<< I disagree. "number" is the direct object, "of complaints" is the indirect object. The verb tense matches the direct object. (has been a number) >>
Wow, this disregard for a couple basic principles of the English language is funny. For starters, according to you, the sentence doesn't have a subject. All sentences have subjects, whether stated or understood (and don't say it's "there", "there" is an expletive that starts a sentence). Secondly, the verb phrase, "have been" is a form of "to be" which never has a direct object. After all, you can't exist upon something.