I see why you're angry and I would call your T on it but I'd also imagine that the "problem" of your T not taking responsibility for his mail, regardless of your feelings about it, probably is what was discussed? I don't think your T mentioned you, but kept the whole thing on your son's responsibilities and paying bills, etc.? You gave him a way to help your son but I doubt your T mentioned you at all.

Think about it this way, if you and I had the same T and I were to mention to him you had a hard time with feeling he betrayed you, he might somehow help that issue come up when he saw you next but it has nothing to do with "me" because it is not my problem so I would not be mentioned at all. You don't have a problem with responsibility! :-) and so you wouldn't be part of the mail discussion other than it just happens your son's mail was coming to your house because he was too "lazy" to work to get it redirected to his own apartment. You would be a "thing" in the discussion, your house, not you personally and how angry his behavior made you feel; the T knows that's a discussion that should be between you and your son.