you haven't earned it - (Open Letter to Dad, no, Sperm Donor)

Dear 'Dad', no, Sperm Donor,
You've never been in my life, except the short time from when I was 15-17. When faced with the responsibility of being a dad instead of a walking ATM, you told me you couldn't talk to me anymore and you removed yourself from my life. Since then I have gone and done things that haven't involved you. This includes my children. I invited you to my wedding and you didn't bother to come, but you immediately blocked my phone number after I left you the invitation voicemail.
I've heard you've been showing around pictures of my children, that you've never met or been sent pictures of by me, calling yourself their "grandpa".
When I sent you back the packages you sent for them I thought I made my intentions clear. You never bothered to be a dad, you weren't there for my first steps, my first bike, first day of school, first heart ache, you missed my graduation, my wedding,the birth of my son and daughter. You are not dad, there for you are not grandpa. My kids have no idea who you are and I have no intention of them knowing until they are old enough to understand.
They have a grandpa, and it's the man who stood in the position you were too weak to fill.
My kids are not your second chance, they are not your family. Remember who walked out on who.
Your daughter.