You are asking us how to stand your ground, how to get people to listen to you, etc. that is for you to work out in your own life isnt it? Not to sound like a dick, but these are the type of relationships you develope w people, set boundaries and such, let people know who u are. If you havent done that till now, I dunno. Just keep talking about it, when they open up to you, show them proof, rinse and repeat anon. Always talk truth, eventually they will be talking about it and where you can say “see, told u about that.. 3 yrs ago, last week.. etc” dont gloat and deliver more info.
If it were me i would just say fuck it and not look for them to acknowledge anything you say.