Unwelcome Christmas card

It's just thoughtlessness nonnie. Probably the sender was on autopilot, and was just ticking names off a list. Try to forget about it, and don't send them a card ever again.

Nonnie
Condolences to you, that was very thoughtless of them.
This Christmas will be hard enough for you without that.

So sorry Nonnie. I can’t imagine what you’re going through so just send warmest best wishes.

Focus on the people who have been supportive and kind to you and don't give the others any thought. Look forward to seeing your DS3 and DiL and raise a glass to your absent son. Try to focus on all the happy memories you all have of him and every time you remember he lives on in your hearts. Cut the toxic ones out of your life they will only upset you.

This is so sad Nonnie. I’m glad you have close family coming over tomorrow to help you to remember your son on his birthday. Heartfelt condolences from me too, and it’s really hard to imagine such awful sadness.
Someone earlier mentioned keeping a dignified silence and I agree with that. I don’t think you need to write or explain anything. As you bin the card tear it up - it might help a little!
Come back to us - we are friendly and certainly caring. Just cross the other person out of your mind and out of your life. Value all the people you are close to.