Have you sent the good Cardinal a copy of this? Isn’t it in the Bible somewhere that if you have a beef with another that you go to them with it?
That’s in the case of a private beef—because it’s wrong to reveal anyone’s private sins to the public without just cause.
But all the bishops who are committing the mortal sin of refusing to obey Canon 915 are doing so publicly. There is no obligation to correct their sin in private.