I feel like this is an error in the printing of the novel. The verb "belong" can not exist in the passive form. The correct for should be "had belonged."

Where did you get your text from? On Stephenie Meyer's own website, it reads "The room was familiar; it HAD BELONGED to me since I was born." http://www.stepheniemeyer.co.uk/books/twilight/an-extract-from-twilight/ I've found other examples of "had been belonged", and in all cases the rest of the text was full of terrible errors. "Belong" doesn't work in passive form.

"It had been belonged to me" is completely incorrect. What book was this? It might be an ethnic or cultural variant.

That's odd, isn't it? The thing about passive voice is it needs a transitive verb, and "belong" is intransitive. I think the "been" is probably a typo.