"I’m sorry, we haven’t been introduced, " may be said by you to someone whom you don't know or had never met before, started to speak to you .

For example: You go to a party with your friend. At the party, your friend greets his sister. You have never met his sister, but your friend forgets to introduce you. If you want to talk to his sister, then you say, "I'm sorry, we haven't been introduced..." and she will say "Oh! My name is..." You use the passive because it's not your job to introduce yourself, you expect your friend to introduce you two. Also, you'd never say "We haven't introduced each other." :)