Dear …
I can’t even begin to express how hurt and disappointed __(I am/we are)__ by your complete disregard of respect and support during __(my mother’s funeral/the bereavement of my mother’s death/etc.)__.
Was it not enough that __(I was/we were are all)__ devastated over __(his/her)__ death that you had to add to that sorrow? How anyone could act so thoughtlessly is beyond me. If you were not able to, or did not wish to __(play the music/give a eulogy/etc.)__, then why on earth did you agree to do it in the first place? Then to add insult to injury, you didn’t even have the decently to respond to __(my/our)__ inquiries about your no show.
It’s hard to even imagine what is going on with you, __(Name)__, why you would choose to snub your nose at the death of my __(person deceased)__ and at all of us who mourn __(him/her)__. All I can tell you is that your display of disrespect and lack of support not only disappointed __(me/a lot of people)__, but has deeply hurt __(me/us all)__.
Yours truly,