Learn English – when to used had been and have been

This is an old question, but I want to make a point clear:

Yes, the present perfect is used all the time, by native English speakers, in all registers and dialects of English, from extremely informal to very formal. You cannot sound like a native English speaker without using it when it is called for. (It's not like, say, knowing how to use "whom," which you don't really have to do.)

The good news is that, in a lot of places, the two are interchangeable. Moreover, you are likely to use the past more. Also, using the present perfect in the wrong place will sound very strange and sometimes make you unintelligible, whereas using the past in the wrong place may communicate the wrong shade of meaning but will rarely get your listener completely lost. Therefore, I recommend using the past most of the time, then inserting the perfect gradually if you are sure you are right.

To make sure I wasn't wrong, I turned on the TV now to a sitcom rerun. Ignoring other tenses (mostly present) here is my tally in ten minutes or so:

past 31

present perfect 4

and some other past tense constructions:

"lately, I have been having thoughts" "I think that may have missed the table." "oh God, I shouldn't have said anything" "he kept laughing at..."

The problem with this question isn't that it has not received enough attention. It's that it still hasn't been edited to provide the requested context. There's nothing inherently correct/incorrect about OP's cited...

"You had mentioned that your sister had been kidnapped by him."

As pointed out (to the same OP) on a previous question, don't use Past Perfect unless you really have to is a good principle. It might be a slightly contrived context, but we can easily imagine the above sentence being uttered as a "question" (a statement made in the expectation of it being confirmed).

Further suppose the speaker is a detective asking the brother about an earlier conversation he had with someone else. I'm no Agatha Christie, but obviously there could be contexts where the detective needed to know whether that other person was aware of the kidnapping before that conversation took place (or at least, before the point in the conversation that the recounting to the detective has reached).

If the detective had used Simple Past, the brother might interpret the question differently, and answer "Yes" when what he actually meant was he'd mentioned the kidnapping later, not earlier. The entire denouement of a crime story could thus hinge on an incorrect answer to a misunderstood question.

But for most conversational purposes, OP should simply assume that Past Perfect is overused by some non-native speakers, and he should strive to avoid being in that number.