I’m sorry you’re going through this. It sounds like an open wound. When you’ve worked through the anger (for however long it takes) you could reach out to them again and try to talk it through since the estrangement is hurting you.

If the letter was why they moved, it seems like they overreacted or they are being over sensitive. You were being the good son by asking them out twice to discuss it and talking over Christmas. Keep trying. Best wishes.